Why do women get gas in early pregnancy?

I have had increased gas and diarrhea, I also have had cramps for the last 6 days and no Aunt Flo (she is due today). I feel bloated. But I know the cramps and bloating could be and mostly likely are my period giving me a heads up. I do not want to test. I just can't bear another negative test. It sux, I took one in the middle of this past week and negative of course. (I always set myself up for disappointment)... I will probably wake up with Aunt Flo tomorrow. Sorry for rattling on girls, but I do not talk to people about my TTC. They ask to many personal questions. Thx for reading... But why do women get gas in pregnancy? And diarrhea or constipation?