Migraine with aura is well associated with MVP and with PFO. I am assuming you do not have a PFO since you underwent a complete work up before surgery.
I have seen several cases of migraine either new onset or exaserbation after surgery or a severe infection. We don't know why yet but I suspect it is due to the physiologic stress on the body. If you are less than 10 weeks post op you are still healing.
None the less a change in the quality or frequency of your migraines is cause for an MRI of the brain. Please tell your doctor about this and request the same. Keep an eye on the aspirin (I know you do have to be on it) but it might be contributing to the headaches. They most probably will prescribe some short term meds to get you through this or refer to you a neurologist if you don't already see one.
Dent Neurologic Institute