Help, severe dryness problem inside body

My son took Accutane (isotretinoin) (20 mg) for about 2 weeks. Shortly after starting it, he developed significant dryness and discomfort. He stopped the medicine about 35 days ago, but symptoms are still present and fluctuate in severity. Eyes: He has dry and sometimes painful eyes. Eye drops provide temporary relief. He feels the left upper eyelid is producing little/no oil or no tears and feel pain in the eye, doubts about MGD. His eye examination showed 6/6 vision, normal fundus and normal eye pressure, with dryness diagnosed. Internal body dryness: He has persistent dry mouth and throat with very less saliva in mouth, sticky/dry lips and dry nose, with a feeling of dehydration even after drinking ample water, like body not retaining moisture and problem in mucus membranes.Sometimes he wakes during sleep because of dryness. He experiences heavy breathing and internal dryness problems. Guide us about any specific solution or medication for these issues or any test perhaps.