Could i be pregnat

Me and my partner have been having sex for about a month almost two with and without protection...this last week we did missionary and i believe he came in me twice and we werw not wearing condoms.....my period is suppose to come on the 28th...should i be worried about being pregnat...he has a child already his swimmers work....never have i been pregnat so i don't know when and if i should freak out.......