Birth control pill question!!

I’m trying to make love with my boyfriend. He wants to cum in me for the first time but I’m scared to take the pill. I heard it changes your body and messes up your cycle also you’ll get mood swings. Is this true? Can you buy the pills at a store like Walmart? I have no other choice but the pills because I can’t talk to my mom about putting me on birth control. She’s not someone I can talk to about it.