Welcome to the forum!
There are a couple of things which you need to do if you desire the help of members of this forum with this issue:
1. Go to the introductions section of the forum to tell us all about yourself and any pets you have. This will provide valuable background, as well as being part of forum etiquette.
2. Please give full background information on this thread about your dog (you didn't mention his/her name): age, breed type (or nearest breeds if mongrel), previous health history, character traits, what food you are giving and how often, whether the dog is eating and defecating normally, whether the dog is drinking fresh water normally, how long you have had the dog with you, whether there were any previous caretakers....etc.
To be honest, without such information we would only be guessing "in the dark". There could be many possible explanations.