Three months without period!

Okay, so I'm looking for some advise or opinions on what is going on! I had my period in January.. Everything was fine. I went the whole month of February without having one though. I thought it was due to stress cause I was having a rough time. Then I had my period March 7th and it lasted about 5 days. My problem is.. I haven't had a period in three months now and idk what could be causing it. I usually have pretty regular periods and I have never went a month without having my period before. Until February of course and I am 26 years old (almost). My boyfriend had a vasectomy about three years ago so I'm not on any birth control, but I've taken like 6 tests and they've all came back negative. 😒 I have a doctors appointment Thursday, the 9th so I'm sure I'll figure it out then. I just wanted to see if anyone has been through this and to see what their outcome was? Thanks for reading. (: