Bleeding the day after sex

Last night I lost my virginity to my boyfriend of 5 months, really glad I did it, but today I woke up with a good amount of bleeding and cramping, at first I thought he hit my cervix because it was my first time and I wasn't used to it, but the cramps& amount I was bleeding was similar to when I get my period(I have pretty bad periods), app says I'm not supossed to get it for 5 more days but I'm kinda irregular. I fell asleep for a few hrs today and when I went to change my pad I noticed I stopped bleeding and my breasts are really tender (thats a normal thing for me but they hurt more than usual). Durring intercourse we used condoms and he pulled out even w/ the condom and I finished him off that way, so I know no sperm got anywhere near &I'm not really worried about that. Anyone know what's going on here? Btw I'm only 16 and I'm really not trying to go to a doctor unless I absolutely NEED to.