Windgalls can be found in front or behind the fetlock or just above it in horses which have been worked hard, they are most common behind the fetlock. They are caused by general wear and tear in older horses or in young horses which have been worked too hard for there age or done too much work on hard ground. Their bursal sack has streached and enlarged and cannot be repaired. Pressure bandages with padding put over the windgalls can make you think they have done some good because when you take the bandage off it can seem as if there is now no filling. In practice though as soon as you use the horse they will come up again. Occasionally the very large tightly bulging windgall will cause unsoundness but the small ones found on very many animals of middle age are of no consequence, they are counted as a fault in the show ring and can detract from the value of a horse but rarely cause problems.
To help your horse cut down the hard work on the hard ground and work him maybe for less time or spray the ground say in the field with water or set up sprinklers for a few hours over night, you have to spray sandschools to in summer because it puts extra pressure on the horses legs to walk on dry sand just as it does humans where as wet sand is more firmer so it would only be the same thing as people with schools have to do. As I said you can't repair them because the damage is already done but you can stop it from getting anyworse and you can sooth them as you are doing by hoseing after work and putting cream on could help as well. Try adding celery to the feed as this will help inflammation as well.
if it turns out to be windgalls try putting arnica cream on the joints and garlic supplement in feed :-)