I Had Unprotected Sex 12 Weeks Ago. I've Gotten Periods

I had unprotected sex 12 weeks ago. I've gotten periods since then but they are lighter and shorter. I haven't felt good at all. My stomach is bloated I was constipated before, I'm nauseous on and off. I have terrible back ache and now I have pain in between my thighs what feels like growing pains. What is this??