What Causes Abnormal Vaginal Bleeding With Stomach Cramps?

So i just finished my period last week which only lasted like 3 days (late Wednesday night to sometime Friday) then stopped completely(Saturday). when i woke up i had a stomach ache that lasted all day. it wasn't a cramp either but just stomach pains that ranged from very a very light stomach ache to a medium pain. Nothing to bad where i couldn't block it out if I was occupied. then I spotted very lightly for about 1 more day.

I took the one step plan B pill cuz because i had sex that day it stopped.(Saturday)

...the pill was taken on Sunday. And today while out i got this sharp pain on like... i guess my clitoris? then when i got home to take a shower I was bleeding as if i was on my period and now i have light cramps. I've taken this pill before and nothing happened. so is it side effects or am i pregnant? with my last period as irregular as it was.