I'm thinking of using Birth Control pills, Im new Please help!

So I'm thinking of taking birth control pills, but Im hesitating because I'm not sexually active, my boyfriend and I usually have sex once a month, and if we are lucky, twice a month. I just really want to be careful, as for now I don't really want to be pregnant. I'm not ready for a baby yet. Last month I missed my period, but it was negative. And today we had unprotected sex, stupid I know. But he didn't cum inside me. (Bad excuse I know) we usually use condoms all the time. It was just today that we didn't have condoms, and we were really on. From where I am, we don't really need prescription to buy birth control pills, you can just ask the pharmacy and they will give you. So not a big deal about that. So should I take some even though I'm not sexually active?? And any side effects I should know before I take it. And any suggestions related to it please.