This is Dr. Christian. Welcome to JustAnswer. A few questions will help me get a clearer picture of the situation:
Typically a hotspot is caused by an allergy but the only way to know for sure is to do some testing. He may end up needing medications from your vet such as antibiotics and steroids since this has been going on for so long. However, her are some other things you can try:
If you have more questions please let me know.