Sorry your period is so late. I had really long cycles for a while as in I'd get periods every 3 to 4 months! My thyroid was working slowly causing this. It was a huge pain because I'd get PMS at 3 weeks into the cycle like it was going to be a normal one and the PMS would last until I'd finally get my period. ugh.
So, reasons why women are late/have long cycles include being sick, stressed, changes in routine, gaining or losing weight, hormonal abnormality, or thyroid issues. I'd wait until it's been 3 months for a period and then see your doctor to determine. That you went off the pill, that will also potentially cause disruption in your cycle and being regular. But doctors like women to have periods every 3 months and that is kind of the jumping off point for them to take you seriously. You've ruled out pregnancy though with a test I presume?
I should have also said that since I started having sex (September 2017) my periods were irregular but only by 2 weeks maximum January 6th-11th was when I had a very light but last proper period 22nd-24th January I had a light/brown blood showing in my underwear since 24th January I've had absolutely nothing and get extremely bad pain in my stomach and back pain.