hi, i can understand your concern..u ve said that u have throbbing pain and it is unbearable, i want to ask you that during pregnancy whether u have been diagnosed as pregnancy induced hypertension means whether your blood pressure shoot much high? because throbbing headache is mostly due to high blood pressure and for your kind information BP goes very high during sexual activity and also during any strenuous activities like u said during defecation. i wll suggest u that u shud go for BP monitoring morning and evening for a week and then for medication if it came high, if it is blood pressure then with medication it will get controlled and u ll be relieved. if is not so then u can consult your gynecologist or general physician for your headache..i think this advice will be helpful to you. best luck