Lost my virginity and have been sexually active with the same person since

I lost my virginity and I’ve been sexually active with the same person since I lost it, we were both virgins. I am on the Nexplanon for birth control however we don’t use protection because we don’t have any and my nexy causes irregular bleeding because I just got it in about the last 3-6 months. This leads me to my question, today we had sex (after twice last night within a half hour) and I am bleeding right after and am experiencing some discomfort down there and was wondering what it might be from. He is fairly small but I’m also fairly new to sex and was wondering what could cause it. This isn’t my first time but I also am not sexual active often apart from when I am with him in which we do about 2-3 times a day. Could it be over working myself? I don’t know if this is TMI but I’m not sure who else to ask because I am 18 but my family wouldn’t take it well if they found out I was sexually active and I have no close friends I want to bring it up with. Any help or information would be extremely helpful! Thank you!!