Thank you for writing!
Oral sex has no effect on the menstrual cycle.
You may be experiencing a hormonal imbalance. You have not mentioned your age but if you are over 35, this is not uncommon. If under 35, it could be due to hormonal conditions like polycystic ovaries or some other imbalance. Stress can also be a factor.
See your doctor for a blood test where your hormone levels can be analysed. Ask for your thyroid (another hormone) to be tested at the same time.