Hey,
I was also on BC since I was 15 (I am 20 now) and I got off, thinking the same thoughts as you, I figured that I couldn’t get pregnant right away since I was on it for so many years. Come to find out BC leaves your system within 36 hours (my OBGYN/Baby lady 😉 gave me all the info) and you can get pregnant within the first month!
So, with that said you should take an HPT test. But, it could also be that your period is going back to its normal cycle and getting back into the swing of things with your body, if that makes sense. Basically, you can end up getting different menstrual symptoms after getting off of BC, thats what happened to me. But, if you are going to stay off of BC and don’t want a baby, use protection. Because 2 months of being off of BC and I am now 12 weeks pregnant with my first child!! 🙂
Good luck to you!