please help

I dont know if I sound stupid but I could really use another opinion, especially as my SO doesnt think its a big deal. so my SO and I just had anal sex and he came inside me and when I went to clean up, I was cleaning around my labia and found some white secretions. idk if it was from him or me but I cant help but worry. I'm not on any kind of birth control, and obviously we didnt use a condom. my period is also going to start in 4 days. should I take plan b?