I've had radical hysterectomy and stopped taking estergen for few months. i have hot flashes and tired all the time. is it ok to start back on them ?

Ask your doctor: If you really had a radical hysterectomy, it was probably for cervical disease. Not unusual to experience hot flushes and menopausal like symptoms afterward just related to stress of the operation. Removing ovaries not typically part of radical hysterectomy so your ovaries may recover. If your ovaries were removed, then estrogen should be ok. Estrogen not related to cervical disease.