Hi thanks for asking question. While going to doctor what was your blood pressure before starting diuretic?? Here you have high blood pressure. You might have skipped dose of drug so that rebound headache can occur. Because of high blood pressure also headache can occur. So continue with taking drug regularly. Low salt diet taken. If headache troublesome analgesic can taken like brufen or paracetamol. If you have associated congestion by viral infection then also headache can occur.for that decongestent taken. Avoid some triggering favor for headache like....loud noise, skipped meal, dehydration etc.... If still bp increasing then consult doctor for taking sodium nitroprusside or other suitable drug by iv route. I hope your concern solved. Take care...... Dr.Parth Goswami