I get being stuck on the diagnosis. The label shouldn't matter bc these are all just brain disorders that the AMA decided to name different things based upon rather subjective criteria printed in a manual that keeps changing. But. It still does matter for some reason.
At least it does for me so I can sympathize.

My current pdoc depolarized me- he disagreed with my last pdoc re the BP dx. So I am back to having MDD. Yet my symptoms haven't changed any. I think it depends on how you view BP- the spectrum model of mood disorders would view recurrent atypical depression to be closer To the BP side so mood stabilizers would prob help more than just ADs. If you view them as completely diff disorders than that wouldn't be the case.

I don't think a 4th opinion would hurt, and maybe it would give you some peace of mind. TBH I think a lot of modern psychiatry is complete bullshat and the whole labeling and over medicalization of emotions is out of control. But if gettinga certain label helps you find the right treatment than I suppose it is worthwhile. Good luck.