HELP!

Okay so I got on birthcontrol about 3 weeks ago but they said that it wouldnt fully kick in for at least two weeks but a few days after I got the shot me and my boyfriend had sex and he finished Inside me. And like a week after that it happened again. So should I be worried or no? I mean I've had some cramps for a few days not super super bad though and I spotted a little last week and yesterday and today. Should I take a test and be sure or should I be fine?