Missed period, recently off birth control

I'm 18 and I recently stopped taking birth control a couple months ago, I got my 1st period after I stopped taking it on time, but I have missed my 2nd one since then. It has been a month since my missed period and I am currently on the week of when I should be getting the next one if I had gotten my last. I have taken 3 pregnacy test all negative, each taken in weeks apart from each other. I just wondering if this is normal after getting off of birth control or if there could be something wrong.