Thank you for your query.
FIrstly, if you never had painful intercourse earlier, but have it now, there is possibility of a pelvic infection
or an ovarian cyst
that is leading to that.
After vasectomy, unless the procedure is deemed successful by having a semen analysis
, you cannot be sure.
Yes, chances of pregnancy would exist, particularly with your irregular cycles.
Go for a pregnancy test or consult with your doctor to confirm pregnancy.
Also the consultation would show you reason for pain during sex.