Some antidepressants really fuck with your libido. So this indeed could be your problem, although you being able to orgasm by yourself doesn't match what I've heard.
Without trying to sound rude, I've been there myself: This could also be caused by excessive porn consumption and having your brain being wired in a way in which masturbation works well and sex being difficult for orgasming, despite feeling good.

It was, yes (no longer on). Everything else was fine but I just couldn't "get there".

That can be a side effect, yea.

For me Prozac basically made it impossible to get hard, it was brutal and lead to some awkward moments. Other antidepressants are better but lots have the same possibilities.