im not sure how old you are now - but yes, i believe you COULD be pregnant. on the other hand, it is not uncommon for women as young as their late 30's to begin experiencing irregular periods. i would take a test, and if its negative, call your doctor or midwife if you continue to be concerned.
Not to scare you but sometimes things happen like this. My bf's friend at work has been told that medically he cannot produce sperm. His gf had her tubes tied and was also told that she will never have another child due to other female issues. They are now 4 months pg with TWINS! Get a test...cause STUFF happens. I hope you get the results you are aiming for.