Possibly pregnant?

I’m 17, and the last time I had sex was last night. My boyfriend came in me 4 times. My period was supposed to start Friday and didn’t. About 3 weeks prior to Friday we had sex and it was possible that cum got in me. I have been feeling just unbalanced hormonally and I’ve been very emotional and having mood swings. I’m not stressed about it and I’m not scared. I have taken 2 tests so far before last night and they have been negative. Is it possible that last night could have gotten me pregnant even if I am supposed to be on my period?