sex 4 days after period

Hey guys!! I'm so paranoid lol please help...so I ended my period on 10/27 and I had unprotected sex on 10/30 but pulled out now today 11/2 my lower back hurts and so do my thighs and legs as if I'm getting ready to have my period...I just wanna know if this is normal?? Has this happen to anyone before? Please help lol I need a peace of mind.