Sexual regrets?

I really struggle with regretting someone i slept with. I was 16 and stupid just broke up with my ex and really vunerable. I didn't want to do it deep down but never said no. Happened once or twice and we broke up after about A month. I feel like such a bad person and hardly no one knows about it. I've been with 5 guys (age 20) all under age of 18. Haven't had sex in 2 years nearly because I'm so upset and feel so ashamed from sex before. Anyone else fm feel like this? It's ruining my relationship of a year :(