Why must pms be the same as early pregnancy symptoms. :(

I had sex November 25th my cycles are usually 26 to 28 days. We did have unprotected sex and he ejaculated 4 times inside me. We arent trying but we are also not against it. Starting on Thanksgiving night I had cramping. I WOULD assume that was a sign of ovulation. I know sperm can live up to 5 days inside the vagina given if * environment for sperm to live is good* ive been having tugging feeling on my left side. I also had very very light spotting this morning. I woke up and could smell everything and nauseated. Also noticed that Ive been extremely fatigued. I know it could also be pms. But the symptoms started on Thanksgiving and have gotten worse up till today. Anyone experience similar symptoms and got a BFP.

Update:

I keep having mild cramping and very light brown discharge..looks like old blood my period isn't due till the 16th. I dont spot before periods... could this be an early sign?