Pregnancy question

6yrs ago with my first born son I didnt know I was prego bc, I was still hving my normal period cycles. I found out tht I was 3 months prego with him when I whent to the doc for a bad headache. . But i didnt stop hving my periods untill i was 6 months prego. . Does anyone think bc tht happened to me with my first pregnancy that it could happen again if I get pregnant again?