What breed is he? How long have you the pup? Where did you get him/her? Were there any shots given prior to you getting the pup? And, last but not least, who sold/gave you a 6 week old pup in the first place! They should stay with the mom until at leas 9 weeks min.
The breed was already stated as "redbone". It is a breed of coonhound. 6 weeks is very young for the pup to be away from its mother. It probably has not had sufficient shots to protect it from the many dog diseases that can cause your pup's symptoms. Please take it to a vet right away. Some of those diseases are easily treated but left untreated will kill the pup very fast.