Pain After Sex

Tristan
So I had sex with my boyfriend for the first time without a condom (we'd done it several times before with condoms) because I've had the Nexplanon birth control implant for two weeks, and I've been feeling a painful burning kind of feeling since then and I was wondering why. I was thinking it's probably because it's been about a month since we had sex and we kinda just went for it. What do you think?