I had awful migraines during peri menopause (I too had cycle migraines) but once through they pretty much dissappeared unless sleep deprived. (Luckily I didn't start HRT as my cancer started at this time anyway) I was worried about starting letrozole for the same reason but have had no issues.
Things that help me is really good hydration, neck massages and if all else fails phenergan ...as it is an antihistamines (migraines associated with histamine ) and helps with nausea. It wipes me out though for a day of sleeping even at only 10mg.
Try to be conscious if you are unknowingly hunching your shoulders since the op. I found I was doing this as tense. So relaxation techniques and post op exercises helped too.
Hope things improve soon.