I have what I've been calling "inverse PMS". First off, I have always had an irregular period. There's typically a 2-3 month break between periods. I don't keep the best track of it. I usually bleed heavily for about 3 days with lighter bleeding after.
For about a week before my period, I become very focused. I'll feel mentally sharp, energetic, able to plan things and carry out those plans, and find it easier to complete everyday menial tasks. I generally feel like I wish I would always feel. By the first day of heavy bleeding this has all faded away into my period fatigue (I'd hibernate if allowed). From the end of my period on I feel a general sense of depression: lack of energy and focus, muddled thoughts, difficulty completing tasks or taking on projects.
The change is so dramatic it feels like I'm switching between being two different people. Any idea as to what is responsible? I worry that if I take birth control, I'll be stuck in the depressed portion of my cycle.