Help a girl out!!

Me and my boyfriend had sex 3 days ago. We used protection and I’m on the implant. After we finished there looked like there was cum on his penis bellow the condom and I don’t know if was mine or his. I’m over worrying that I could be pregnant. I’ve had a few stomach aches within the 3 days and I don’t know if it’s just general aches. I’ve not had a period in 2 months as the implant has stopped them at the moment. What should I do? Also when should I take a test?