I think you left a number out of your OP. How many months ago did you wean? How often were you pumping before you quit? Was it a gradual cessation?
It is common for periods to be irregular when bfing. It is also common for lactation to continue for up to a year after weaning. Sounds like you are having some hormonal fluctuation.
If you feel engorged, express a little milk just to the point where you are comfortable.