It stands to reason, IMO, that if your life is a heap of steaming shit, then you don't need to have a preexisting neurochemical imbalance to be depressed, the simple fact that one say, lives in a third-world shithole, in constant pain picking rice for a living, and has had a leg blown off by a landmine sounds like more than enough to make one depressed.
Also, there is such a thing, neurologically speaking as 'kindling', its related to 'use it or lose it' in terms of synaptic pathways and connections, those that are not used get pruned, and those that are used strongly and constantly are strengthened. Thus, as they say in epileptology, 'seizures beget seizures', and it would make sense that a person who ends up depressed undergoes biochemical changes, and as they stay depressed, the worse it gets, the more the re-routed synaptic connections induced by such changed are strengthened.
Elle, you have tried conventional antidepressants with no luck, haven't you?
Here is a suggestion, it'll require consultation with a specialist, and its an inpatient procedure (brief in-patient, in and out the same day, a few hours most likely), but for highly treatment-resistant depression, ketamine therapy is now recognized, and it is given via infusion or injection, and can have VERY dramatic effects, on people who have been there and tried that with more or less every typical antidepressant under the sun, within hours, and which lasts for a long time after a single infusion (many weeks to potentially months, so it would be an occasional visit to a clinic for top-up procedures), and seems to be a property of ketamine's action on mTOR (mammalian target of rapamycin), and more specifically its metabolite, hydroxynorketamine. The effects, as said, are long lasting and have proved in many cases to nearly to completely reverse the depression in very severely depressed patients who have proven resistant to everything thrown at them in terms of more well known antidepressants.
Just thought I'd throw this out there for you, in case you were not aware of it.
Also, whilst it isn't available on prescription in the US, its widely available online.
Another highly atypical antidepressant, tianeptine (originally classed as a selective serotonin reuptake enhancer, this was later found not to be the case, with little or no affinity for SERT)
https://en.wikipedia.org/wiki/Tianeptine (amineptine is a relative of it, but probably is best avoided as it has some liver toxicity potential), it does possess a slight to modest abuse potential, but only at very high overdose levels, and usually when misused by intravenous injection. It appears to be a mixed Mu-opioid receptor biased agonist with some effects at delta-opioid receptors, along with being a modulator of glutamatergic (NMDA receptor, as with ketamine, and AMPA type ionotropic glutamatergic modulation) and appears to prevent stress-induced (chronic stress is closely linked with depression) remodelling of synaptic pathways in the brain)
One other idea, would be an AMPAkine (avoid if you are seizure-prone or epileptic), of the high-impact type (sunifiram, aka DM-235 for example is available online as a nootropic, doses should be kept at or below 5mg), excessive doses can lead to excitotoxicity and seizure, but at 5mg it appears safe, drop the dose if headache and nervous tension appear), this should have both nootropic and antidepressive effects via BDNF increased expression (brain-derived neurotrophic factor) and corresponding TrKb activation, which promotes neuronal differentiation and survival, and has strongly anti-depressive effects. Also AMPAkines are primarily known for their facilitation of learning and memory consolidation and retention. I plan to start on it myself as soon as I get round to buying some more piperazine with which to make it. (it is buyable, but I can probably reduce the cost to myself by making it in bulk, after first trying a small amount bought to see if I respond positively or not to it, before committing both the time, effort and reagents to make the stuff)
The ketamine therapy in particular-read into it Elle, you might find it worth pursuing based on what you find, the results have been extremely promising and dramatic in improvement in some seriously treatment-resistant depression cases, and it requires only redosing as a single-dose top-up every few weeks to a month or two, so only a relatively few treatments yearly. Memantine, another NMDA antagonist also has some quite strong antidepressant effects in my experience with taking it, and unlike ketamine, it specifically targets over-active NMDA receptors, as an uncompetitive NMDAr antagonist with rapid on-off binding kinetics and relatively low affinity, and whilst HUGE doses can produce dissociative effects, it requires a quite deliberate intent to do so, the difference between a clinical dose and a dissociative dose being 10-20fold (hundreds of milligrams rather than tens) higher.
Very low doses of the antipsychotic amisulpiride (below the antipsychotic dose) act on GHB receptors and induce glutamate release, in moderation, and have been reported as being of an activating antidepressive profile.
And lastly, entraining your circadian rhythms also is well-known to have antidepressive effects, and at worst, helps in boosting the efficacy of antidepressive therapy, melatonin and agomelatine, the latter being another atypical antidepressant drug with similar effects to melatonin) would be the best way to achieve this. If you go for that, avoid the melatonin supplements with a few hundred micrograms to a milligram or two, these are ineffective more or less, and its best used at at least 10mg orally), if nothing else, melatonin coupled with deliberately timing it with going to bed at a specific time is most certainly not going to harm you. Even cases where hundreds of milligrams have been taken, the most dramatic effect has been sleepiness, without overt toxicity of any kind resulting)
Just thought I'd throw these out here for you, in case you are unaware of any of them, in the hope that one or more of them may help you. We might have had our differences before, but I would far prefer to see you happy in life than unhappy and depressed.
Again, just throwing these