A lot of factors, including stress, can cause changes in cycles. Depending on your age as well, cycle changes can occur with menopause and even early menopause with some women. It's very unlikely to be pregnant after tubal ligation, I can't say impossible, but still extremely unlikely. Changes in medications, diets, new workout routines can also affect cycles in some women.
For peace of mind, if you are late, take a test and you will know for sure. You can also make an appointment with your primary care doctor if you are concerned about your symptoms.
Good luck.
Well thank you im going to do a test to see today and I still havent got my period I welllet you now if iam or if its something else thank you for replying back