can I get pregnant?

My last period was on April 25, 4 days ago I took a pregnancy test at the doctor's (for surgery) & it was negative. Then 2 days ago, I had protected sex but he stayed in me for a bit as he was going soft. I think he's aware that sperm can get out so he pulled out & we checked the condom to make sure it didnt break & it was good. My period is really late & so was my last one but now I'm worried if it won't come at all because what if some sperm got out? It was 2 days ago so it would be too early to take a pregnancy test & other than that, I can't be pregnant cause aside from recently, I haven't had sex since February 
Also, can a period go from regular to irregular?