Headaches following radical hysterectomy

Help! Since my surgery, I've been having migraine-like headaches on a regular basis. Prior to surgery, I'd have a migraine maybe once a month (usually during menstruation), and a "normal" headache here & there which could be relieved with over the counter meds. My oncologist said the headaches were due to a lack of estrogen, and he prescribed Premarin which helped for about a week, but now they're back. I'd just as soon not take HRT, especially if I'm still having the headaches. The info. I've researched on the web is all over the map on this topic. Has anyone had this experience or have any info.? I'd greatly appreciate any help. Thanks!!!!