Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. If you feel his dehydration is still persisting you can take him to ER, get him admitted again for IV fluids. Detailed evaluation with blood test, sputum test, chest X-ray has to be done to find out what is the cause of chronic cough. Backache may or may not be related to cough. If backache is due to some reason other than chronic cough then, he has to consult an orthopedic doctor who will take an X-ray and do detailed examination. The most common causes of a chronic cough are: 1. postnasal drip 2. asthma, especially cough-variant asthma, which causes a cough as the main symptom 3. acid reflux or gastroesophageal reflux disease (GERD) 4. chronic bronchitis or other forms of chronic obstructive pulmonary disease (COPD) 5. infections, such as pneumonia or acute bronchitis 6. ACE inhibitors, which are medications used to treat high blood pressure 7. smoking Less common causes for a chronic cough include: 1. bronchiectasis, which is damage to the airways that causes the bronchial walls in the lungs to become inflamed and thickened bronchiolitis, which is an infection and inflammation of the bronchioles, the tiny air passages in the lungs 2. cystic fibrosis, an inherited condition that damages the lungs and other organs by causing thick secretions 3. interstitial lung disease, a condition that involves scarring of lung tissue 4. heart failure 5. lung cancer 6. pertussis, a bacterial infection which is also known as whooping cough 7. sarcoidosis, which consists of clusters of inflamed cells, known as granulomas, that form in the lungs and other parts of the body. He may need to have one of these tests to find the cause of your cough: 1. Acid reflux tests measure the amount of acid in the fluid inside your esophagus. 2. Endoscopy uses a flexible, lighted instrument to look into the esophagus, stomach, and small intestine. 3. Sputum cultures check the mucus you cough up for bacteria and other infections. 4. Pulmonary function tests see how much air you can breathe out, along with other actions of your lungs. Your doctor uses these tests to diagnose COPD and certain other lung conditions. 5. X-rays and CT scans can find signs of cancer or infections like pneumonia. He might also need an X-ray of your sinuses to look for signs of infection. Hope I have answered your query. Let me know if I can assist you further.