My boyfriend came in me 2 nights ago. According to my app I had a low chance of pregnancy but the day after it was a medium chance. Could I be pregnan?

Not reliable. if pregnancy is on your to do list ,then keep taking chances by having unprotected sex, and by not having a plan to protect you from pregnancy. the counting days method is not reliable. if it is not then practice safe sex, even if you have one partner, and see a doctor to place you on birth control plan. there is a lot of bad disease can be spread from unprotected sex. be smart protect your future.
YES. unprotected sexual intercourse will ultimately result in pregnancy. If you are old enough to have sexual relations, then you are old enough to use double protection: condoms PLUS- spermicidal jelly, foam, sponge, eggs, or BC pills. Time to see your GYN and do a pregnancy test.