I got my period three times in one month and now I haven't gotten it in 5 weeks. Does anyone know what could be wrong?

Don't worry I have gone to the doctor and he sent me for blood testing but I can't get in for another month. So I am just wondering if anyone has any ideas of what could be going on!

I got my period three times in a month (Feb 14-20, Feb24-28, and March 8-13) and they were full periods. But now it has been just over 5 weeks and I haven't gotten it again. I have been trying to figure out what I have been doing differently and this is all I could come up with. Since I haven't gotten my period I have taken like 10 pregnancy tests and they are all negative!

- I had to restart my birth control in November (I was extremely sick for a month straight and never took it so I had to re-start) and I missed one day of it at the beginning of February but missing one day shouldn't have affected it this much

- I stopped taking antidepressants in December

- I started smoking week at the end of January and I do drink and smoke a bit (not sure if pot could be a factor)

- Or it could just be stress with university as I have been overwhelmingly stressed since January

Like I said I have an appt next month for blood work but I was just wondering if anyone has any ideas on what it could be :)