Thanks for the quick response.
There are many things that can cause constipation in little dogs: Gastrointestinal upset, mild dehydration and reduced mobility. Another thing that can cause constipation is filled anal sacs due to discomfort associated with defecation.
These types of things can cause lethargy and depression, but I would watch her closely to make sure it is not something more severe. If she starts having severe vomiting, or passing dark tarry or bloody stool, stops urinating
, or develops severe vomiting she should be seen by a vet as soon as possible,
If you have a rectal thermometer you can check her temperature. A dog's temp should be between 101-102.5 F. If she has an elevated body temperature she should be seen soon by your vet as she may have an infection or some other medical condition
A few things you might try to reduce constipation include adding a bit of canned pumpkin (1 teaspoon/day) to her diet, along with the same amount of active culture yogurt. If you do this consistenly you might find that she has a solid and normal bowel movement regularly. I would also have her anal sacs checked and emptied periodically.
If she does not have a bowel movement in the next 12 hours you might want to try a warm water enema with a bit of liquid soap like dawn dish soap to make it slightly sudsy. I would not use more than 1 tablespoon of fluid to give an enema in a dog her size. If she still has no bowel movement within 24 hours she should be seen by your veterinarian.
I hope this helps
Please feel free to ask any follow-on questions you might have.