I can empathize with you. It can take years to find the right diagnosis, and combination of medications that is right for you. That sounds disheartening but it is most important that you persevere.
I am not a medical professional, but some of the sypmtoms you are describing do sound like bipolar disorder. The Seroquel used to be prescribed for schizophrenics (and now also for manic bipolar sufferers), and that may be why you are feeling detached, and unable to 'recognize' yourself or to identify and articulate what you are feeling (even though you did well in your post here).
Your seroquel dose sounds like it is in the high range, and that may be the cause of your weight gain. Depakote is also usually prescribed for bipolar disorder. The prozac dose you are on is close to the minimum (20mg I think) and sometimes prozac and other anti-depressants can reduce in effectiveness over time as you build up an 'immunity' to it.
In my experience, when I first tried prozac I went into this extreme manic state that lasted the entire time I was on it. At first, I loved it, I thought, finally I'm normal and thank god I now longer what to kill myself. But looking back I was way out of control. It actually induced mania in me.
I've tried a range of anti-depressants: tricyclics, SSRIs, NSRIs, MAOIs. As well as anti-anxiety meds and mood stabilizers. Sometimes on their own, or in combination.
I too got addicted to the mania, but at the end of the day, being uncontrolled and making bad decisions and acting on impulses can be destructive and have long-lasting effects. It is possible to be stable, but to also have 'natural highs' where you feel genuine joy but also feel sad - the normal cycle highs and lows without the extremes, and this depends on getting the right combination of meds.
I currently take zoloft, wellbutrin (2 SSRIs) and Lamactil (mood stabilizer). I had also been on lithium (mood stabilizer) at 900mg with the other 3 meds, but it was all too much for me and the lithium made me put on weight, feel 'gluggy' and slow. The Lamactil with the 2 SSRIs has worked pretty well for me. Lithium does not cause weight gain in all people, especially at lower doses, so that might be an option.
Maybe sometimes you are experiencing anxiety rather than mania? This could explain why you prefer to be isolated and not interact with others. But as you probably know, isolation and withdrawing is the worst thing you can do right now. And I honestly think that your sister and her family want to see you happy and healthy and that they will do anything to help you.
Especially considering you are going through the extra burden of living in a different country, I'm sure they would do all they can to help. Maybe your sister could come along with you to your psych appointments to help articulate what you are feeling, your history and just for moral support?
Sorry this is long, but I would strongly recommend that you discuss everything with a psychiatrist. If you've been on other meds, then write up a list, including doses, effectiveness and side effects of each.
Good luck and hugs,