Pregnancy Scare on the Nexplanon!!

I’m 17 years old and I recently got the nexplanon (January 14th to be exact). The first day of my last period was January 11th. Immediately after getting the nexplanon, I started having unprotected sex and there were multiple occasions where he didn’t pull out. I had some mid cycle spotting, which I’ve never had before. However, I figured it was a side effect.

Recently, I went to the ER and that’s where they informed me that the nexplanon still needs about a month to kick in. NOBODY TOLD ME THIS WHEN I GOT IT!! I would have been a lot safer, had I known. I just assumed it started working immediately and that’s one of the reasons I opted for it instead of the pill.

It is now February 18th and no period. I’m having light cramping, my lower back is a little sore, and my boobs started hurting this morning. I know these could be symptoms of my upcoming period or the nexplanon in general. With that being said, do I need to take a pregnancy test? Should I be worried?