Is it possible to get pregnant at this time of the month?

Last month I ovulated around the 20th. Two days before my period started, my boyfriend came inside of me because I knew I already ovulated and was about to start my period. There is no way I could be pregnant right? I have been having pregnancy symptoms for about a week now but think they may be all in my head. It is impossible to ovulate again in the same cycle right? But isnt that how fraternal twins are made? Because there were two eggs released? Thanks for any clarifications!