I'd say it's definitely because you're off the pill. When I quit the pill (so that Dh and I could have a baby) I had really bad cramps. Now that I'm back on it, I don't have cramps any more. For most women, the pill makes cramps go away or at least lessens them. Also, when I wasn't on the pill, (before I got pregnant, and before my UC was diagnosed), I usually had a day or two of loose stools (not diarreha) and increased frequency just prior to starting/at the very start of my period. It was also like that before I ever started the pill at age 18.
Symptoms began in November 2008, ~4 weeks after giving birth to my son.
Eased for ~3 weeks in December, possibly b/c of probiotic use?
Returned in January 2009 (with a vengeance), diagnosed with pancolitis on January 30.
Currently taking Asacol (400mg 4 pills 3x daily), Rowasa every other night, Culturelle probiotic, and Zoloft (25 mg).