He is 100% sterile but is there a tiny possibilty? ?

Last Thursday I had sex with my friend, who is sterile. His dr said he had no chance of having kids his entire life (hes 33). Anyways. He asked if he can come inside of me so I said sure. He gets those testosterone shots (I think that's what he said they were). I was at my most fertile last week. I've been feeling nauseous and have been having migraines since. I know this sounds stupid, but could there be a teeny tiny chance of me being pregnant?