pregnancy on birth control

Ok. So im 21 and have a four month old daughter. I started using the birth control pill Nortrel about two in a half months ago. i missed one pill in the second month and have been having sex with my husband since my 6 week postpartum check up. we have been using condoms but not at first. he only puts it on right before he ejaculates or he would just pull out. I have missed my most recent period and im supposed to start another period a week from today. I dont know if i could be pregnant.???????