Painful Intercourse

so, little over two weeks ago I got the nexplanon. My bf and i waited a week to start having unprotected sex, but it's been hurting a lot. I dont think its dryness because we've been using lube. it hurts near the first inner section of the vagina. we've been thinking it could be tears or something. i also know it's not an sti because I got tested before I got the implant and so did he. any thoughts on what this could be?