Am I pregnant?

Okay so I'm on birth control. Me and my boyfriend regularly have sex. Sometimes we occasionally have sex without a condom at the beginning of our sessions. But my boyfriend always tells me to stop and we put on a condom before anything happens. And if we feel like anything is wrong we go get the plan b. Ive been worrying myself sick about being pregnant. I've been really gasey lately. I feel like I'm getting fatter. And I have a question. If I'm pregnant and I don't know it and I keep taking my pills will that cause me to still have a regular period ? I'm scared that I am and I haven't noticed it or something?