I am sorry your boy has this trouble.
It may be his anal sacs or it could be a sprain called Cold Tail.
Please compare your babys tail to these photos:
I printed this for you:
Cold water tail," "limber tail syndrome," "broken tail," "dead tail," "broken wag" are all euphemisms for a relatively common occurrence in sporting dogs. The tail of the dog hangs down from the tail base or is held horizontal for three or four inches and then drops down. A flaccid tail episode appears to be a painful, but relatively benign affliction that can occur after swimming, after a heavy hunting day or even after a bath with cold water or water that is too warm. It is not always associated with swimming or water, but can happen after a heavy day of work that involves a lot of tail action. The majority of limp tail cases have been reported in sporting dogs or hounds -- Labrador Retrievers, Golden Retrievers, Setters, Pointers, Flatcoats, Foxhounds and Beagles are the breeds frequently named. Almost all dogs that suffer through an occurrence return to normal within a few days. Affected dogs may or may not have a repeat incidence during their lifetime. [It is this author's experience that symptoms will repeat in the same animal and can be trigged by something as simple as a cold water bath.] This affliction has been described by the layman as a "sprain," fibrosis or a "cold in the tail." The affected dog is miserable at the onset and the tail is painful. If neither the dog owner nor the veterinarian is familiar with this condition, it can be disturbing
Here is the rest of the link:
If it is a sprain it will heal without treatment.
If its his anal sacs they may need to be emptied. Any vet or groomer can do it for him
If he develops any abdominal pain, bloating, constipation or cannot keep anything down he needs to be seen by a vet.
Please let me know how he is doing. I will always be here for you
I hope your baby feels better very soon..