I think the effect of the pill should definitely be researched further. This may be tmi, but I always had a slightly more sensitive GI tract during my period - more frequency and looser stool. It always resolved after the first couple days.
I started taking the pill in September of last year, when I was 26. I first noticed I was incredibly fatigued, but I've always been slightly anemic, and I'm vegan, so I wrote it off as not eating enough iron. Looking back on it, being on the pill should have actually improved my anemia. Loose stools, frequency, and urgency soon followed. I started taking iron pills that also apparently irritate the GI tract. Some blood appeared in January, and my inflammation markers spiked in April.
After I was scoped, the GI saw skip lesions likely secondary to Crohn's, but the biopsies were much milder than what he saw. I started taking Lialda, which resolved the loose stools, but didn't cut down on the frequency and only slightly decreased the urgency.
Anyway, I stopped taking the pill on June 25th. Things were going fine until I noticed a fistula reopen (which had initially appeared a month earlier) almost 3 weeks ago. Flagyl and Cipro did nothing to clear it up, and I stopped those over a week ago. Well, I got my first normal period 5 days ago. Frequency increased, but the urgency and looseness didn't, and the fistula stayed the same. Today should be the last day of my period. Yesterday I only went to the bathroom twice (literally the first time that's happened since September). Today was the first time I had absolutely no urgency in the morning, and my fistula is almost completely dried up.
I know there's a spike in diagnosis around my age, and studying medicine makes me more vigilant of my health than the general public, but I'm convinced there's some sort of connection.