Help! Should my boyfriend and I stop having sex?

I really need help. My boyfriend and I have been together a year and have been having sex for the past 5 months. We are both seniors in high school and my mom really approves of our relationship. But if she found out we were having sex she would kill me. I really need to go on birth control and have tried going through my doctor and plan parenthood but there is no way I can get past my mom to get birth control. My mom has life360 on my phone so she would notice if I ever went to planned parenthood or the doctors without telling her. But I get EXTREMELY stressed about my period. The two weeks before I get my period I constantly think I am pregnant. I just can’t get it out of my head. We ALWAYS use a condom but the 2% chance stresses me out so much. If I got pregnant I would tell me my mom but I want to preserve our relationship and not ruin it with something like that. My boyfriend hates seeing me so stressed and suggested we stop having sex till I get on birth control but we both really like it so I’d rather not stop. I guess what I’m wondering is how effective are condoms realistically? And how do I deal with the stress of not knowing for sure if you’re pregnant or not? Please help!