Hi!
Having a tubal ligation should NOT interfere with your cycles. I ALWAYS recommend a pregnancy test, so, you should definitely do that. What is more likely though, is that you have irregular cycles that have been masked by your birth control pills.
If you were my patient, the first thing I would do is give you progesterone for 5 days and see if you got a period after taking that. If you did, then I would wait and see what happened next month. If not, I would order some lab work including: FSH, thyroid panel, prolactin level. These are some basic hormone tests that can sometimes explain irregular periods. If you have a tubal, it isn't crucial to have a period every month, but it is important to have one at least every 3 months to prevent a build up in the uterine lining.
I have more than once ended up putting someone back on her pills to regulate her periods after tying her tubes!
I hope this helps!
Good luck!
Dr B