I too experience almost pregnancy like symptoms between ovulation and period. It isn't uncommon, although for me it is rather new. Typically it's hormonal. Sometimes your Dr. can help out, I would see him/her. Of course pregnancy is always a possibility. You can take a test about 3-5 days before your period is due if you use a sensitive one. Look for the box to say it can be used early. Good luck.
Hormonal changes during menstruation can cause all sorts of things...including headaches.
I get a migraines during my period...I even got them when my period would have been occurring when I was using an oral contraceptive to skip my period (since I mostly wanted to skip the migraine and that didn't work, I gave up on the skipping periods thing LOL)