Hi I'm Stupid Help Me

So listen up, I've had my flings here and there, and I've been getting suspicious lately. I have had my boyfriends/partners cum in me LOADS of times (no pun intended). And I'm still not pregnant, not that I really want to be. The whole deal is that when I was 17 I had a serious boyfriend that would not use condoms and accidentally cum in me on a regular basis and I was too broke to buy a plan b and plus I hate taking pills. I'm a natural resolution gal. And ever since then when a guy cums in me on accident I just kind of shrug it off and cross my fingers and my period ALWAYS comes. Now I'm not trying to get pregnant, but my sister has been for years and she's thinking she has something wrong with her baby oven. I'm starting to think there is with mine too which is kind of sad because I know future me, like 10 years from now, might want to get to cooking and that may not be in the cards for me. What do you guys think?