You are taking a major mood stabilizer (Lithium) at a medium dose and a major antipsychotic (Seroquel) at a medium-to-high dose. They should be able to give you an antidepressant without your flipping into mania because both Lithium and Seroquel would protect against that.

Suicidality is another story. What AD's made you suicidal? Maybe the Dr needs to try other AD's. Also, suicidal ideation may be transient as you get used to AD so the Dr needs to monitor you carefully but that is not a reason not to try. You need help for sure.

Another thing is that the dose of Seroquel is significant and one wonders if it makes you depressed by acting too strongly.

Basically, looking at your cocktail I get the impression that your pdoc is not trying to help you live well, but simply is trying to avoid your becoming either suicidal or manic, but does not mind your marinating in this desperate low grade depression. This is an overly conservative approach that should be challenged.