What is going on with my body??

My period has came on back to back twice. August 5-11 was my normal period. Then I had sex I believe on the 22nd and I started bleeding AGAIN. (I figured the sex just started September’s period earlier) So I ended up coming on twice in one month, which wasn’t normal for me. But it was something that was normal based upon research. So at the end of my second period which was the 30th. I had sex again, 3 days later I’m back on. At this point I don’t think it’s the sex. Why am I bleeding so much?