Freaking out!!!!

We have a 4.5 month old son and we are not planning on trying for another for a good year (I want enough time with my little guy before another one joins us). We had sex tonight and I forgot to check when I’m supposed to ovulate. It says I’m ovulating in 9 days (another app says 6). What are the odds that I could get pregnant. Would plan b mess up my cycle at all??? I need advice and support ladies! Please!