Why do I feel miserable after tonsil, adenoid surgery?

Pain and dehydration. These are two thing that can make you feel miserable. Make sure you are taking the pain medication as directed every 4-6 hours and also make sure you taking in enough liquids. Dehydration can really make you feel miserable.
Everybody does. Tonsil and adenoid surgery is one of most painful operations for an adult. If you do not develop any bleeding (about 1%), the pain will require narcotic relief of the sore throat and will probably take 10 to 12 days to resolve. Your ENT doctor should have stressed this.