irregular period?

Hi guys!! so my last period was december 17th-24th (theyre usually long like that) but i haven’t had a period since then. i’m 18 and i am sexually active with my boyfriend but we have always used a condom and we always check for leaks and rips so itsvery unlikely that im pregnant but i’m still confused. Ive taken a few tests and they’ve all been negative and i even got a blood test from my doctor after my first missed period and it was also negative. Both months that i missed my period, around the 17th i would spot very little as well. but never an actual period. i would also get all the symptoms like cramps and breakouts but i never got my actual period. i’m really confused! anyone experiencing the same?