Are you haveing any symptoms of mania besides irritability (which is also a sign of depression)? You sound like me in the early stages of depression, honestly. The irritability, the withdrawal from people, etc. You should probably talk to your doctor about an anti-depressant, if you haven't already. mood stabilizers would be better termed Anti-manics, since they do little to stabilize you on the down side of things. I think the only one that was shown to have any real effect on depression was lamictal. I was on it for about a week before getting the rash from it. However, it definitely helped with the depression. If you're looking to just take one pill, that might be one to look into, otherwise an SSRI or SNRI might be the way to go. But of course only a doctor can tell. I know how you feel about seroquel. 300mg is a big dose. Whopping, really, in terms of what it can do to sleep. Once, when I was manic, and got hospitalized, I was put on 300mg or 400 on my first day there. I then slept for 3 days, woke up, and checked myself out. Since then i've had no manic episodes, but thats just luck. Really good luck. 2 incredibly deep depressions, though.
So, if I were you, I'd talk to a psychiatrist about lamictal and/or about an S(N or S)RI. Both have the potential to help you tons, but SSRIs can cause a bp to become manic, so a stabilizer is neccessary.