What Causes Constant Headache After Hysterectomy?

iam suffering from headache since 2004 after hysterectomy in september 2003. i have seen many psychiatrists and took all kinds of antidepressants.i have also done MRI.test was ok.till now iam still having the headache.sometime the pain is severe and sometime it is less.i want to get rid of the pain completely what must i do?iam still taking antidepressant.1pari cr 12.5 mg in the morning and half lexotanil 1.5mg at night.please help.thank you.