From what you described it sounds like diabetes or Tyzzer's Disease...if it is a dwarf its probably diabetes cuz they're prone to it.
TYZZER'S DISEASE: The bacteria Bacillus piliformis, which is carried by wild mice, causes this disease. It normally affects newly weaned pups and hamsters under stress. It is extremely contagious and usually fatal. Symptoms include lethargy, loss of appetite, extreme diarrhea, dehydration and weight loss. Treatment is seldom successful; but would consist of keeping the hamster warm, sterilization of the cage, plenty of fluids and administration of oxtetracycline under the direction of a veterinarian
DIABETES: Although it can affect all species, diabetes is normally seen in the Campbells Dwarfs and is assumed to be an inherited disease. It generally strikes between 7 and 9 months of age and can be triggered by diet, stress or a dirty cage. Symptoms include excessive drinking and urinating and possibly shaking, trembling and a low body temperature. Severe cases can also result in a coma. Contact a veterinarian at the earliest signs. Although there is no cure for diabetes, steps can be taken to enhance the quality of life for the ailing hamster. For rehydration purposes, with veterinarian directions, a solution of unflavored pedialyte can be given in the water bottle. If a sugar free diet is recommended, the following can be fed: a good quality seed mix, alfalfa, carrots, potatoes and boiled egg. Don't feed any of the commercially prepared hamster treats since many of them contain molasses and corn syrup.
And yes you can take a hamster to a vet. Just call first.