Been on pill for 7 months take it around same time daily, had sex on last day of period he came in me 2 days later have cramps on lower abdomen, why?

Cramping: May be infection check urine, may be vaginitis like mycoplasma, ureoplasma. if though on pill i always check HCG. if persists consider sonogram to check for ectopic or fibroids, polyps. PID. . Could also be Gi from constipation ( try milk of magnesia (magnesium hydroxide) 1 tablespoon 2x a day x 3 ) in young people diverticular disease is rare but ileitis/ food intolerances occur. f/u /w/ doc