Hello I have gone through your question and understand your concerns. Diarrhea lasting for a month with weight loss, symptoms of fatigue and weakness requires diagnostic evaluation. Consider seeing a gastroenterologist at the earliest to get the endoscopy and stool examination done to find out the cause for concern. Till you get an appointment with an expert take precautions on your own like avoid the food that aggravates the symptoms of diarrhea, drink ample of fluids to prevent dehydration, avoid any form of mental or physical stress. Headache and eye pain might be due to eyesight or simply due to loss of essential nutrients. In this situation it is better to get eye checked by optometrist. Hope your concern is answered. Thank you.