post epidural headaches are a fairly common complication of epidural anaesthesia. it was probably explained to you when you decided to have it done.
they usually occur within 3 days and have been reported to occur for as long as 6 months. 2 years is a long time and i'd be thinking about other things at this point.
the epidural is no longer with you and was used by your body. the causes of post epidural headaches is quite a few.
CSF leak (spinal) headaches usually start sooner after the procedure and yours sound like they're quite long after.
Ask your doctor about other kinds of headaches such as migraine, cluster, stress