I had sex whilst on my period, he had a condom and pulled out before finishing

Hi, so im really worried i could be pregnant. So last month i had sex whilst on my period but with a condom. He pulled out before and finished on his own. This was only my 2nd time having sex so it did not last long. Is there a chance i could be pregnant. I cannot remember having my period this month. I may have or may not. If i haven't it should have been last week. I am only 17, is it normal to miss a period. I was also sick last week but the woman at the chemist said that was normal out of the circumstances i told her. I have been stressing a lot as well so i know that could delay my period as well. Someone please help!! I can't be pregnant....!!