Well, I think maybe you are over-reacting and over-analyzing. Maybe try to just let it go. Don't allow a small thing (and common at that) to fester into something it's not deserving of.
Flowing well in a 3 way sexual situation takes practice (so practice more
). Different times different people seem to end up in the center of attention and that's ok. Be happy. Your turn will cum - especially if you just express (in a nice way) that you were ENVIOUS of that particular flow. It's normal. Caring partners will WANT to make sure you get yours another time - and you will.
Don't be greedy - as you said.
Different times different moods and needs are present and that's just one of the facets that 3 way sex and relationships have to acknowledge and work together to balance. Can someone occasionally come out with the short end of the stick ? Absolutely. Such is life. It's only when it happens repeatedly and consistently that it's a problem.
And you are probably right about the meds. Anti depressants are nasty drugs - far worse than most street drugs, and changing routines with them can upset the apple cart pretty easily. Sad fact is that as long as you are addicted to them your life is likely to be........unpredictable at best. But that's not a topic for here.
Learn to flow............