I am 16, and I slept with my boyfriend for the first time

I should have already had my period. I took a pregnancy test to be sure, but I’m not pregnant. Yet I didn’t get my period, and my stomach hurts too.

You should take another pregnancy test a week later (you do not specify the method of contraception). If it is negative, you can wait for the next bleeding, as irregular periods are quite common in your age.