Please help 😔

My SO and I had sex almost 3 weeks ago and we didn't use a condom and I'm not on birth control. Anyways, I started my period last Thursday, lightly and then it stopped (just like when I was pregnant with my daughter) well two days later it came again and it was pretty heavy. I'm still on it but it keeps going heavy and light. Anyways, I feel SO sick, again, like when I was pregnant before. Also, my period was 14 days early! I don't know whats going on. Any suggestions or anything about be appreciated. Thanks!