Possible pregnancy?

First post!
I've been on tri sprintec for over 2 years now, have a regular period every month that lasts about 3 days. Sexually active with my boyfriend, always take the pill as directed. This month I had dark brown spotting for 2 days, and 1 day of a very light period. Cramps have been persistent for about a week now, lingering pain and bloating. Took a pregnancy test that was negative but something tells me something's not right. Anyone ever have similar issues while on the pill? 
Will be calling my ob soon, just want to get others in put on this :)