Can you tell me how old your dog is?
Has there been any vomiting?
Could he/she have gotten into anything - garbage, something outside, chewed up a toy?
Most things that would affect the liver are not directly contagious, although there are a few exceptions to that. It is possible that both dpgs ate something that could be causing similar illnesses though. The symptoms you are describing are fairly general, and just tell me that your little one is not feeling well - they are not specific enough to suggest any particular diagnosis. The shaking/shivering can be a pain response, nervousness, fever, or just a very general sign of not feeling well. The same is true of lethargy. The fact that she hasn't had a bowel movement is probably just because she is not eating well.
Because this is a very small breed of dog, and she has not been eating and drinking, I am concerned that she could become dehydrated very quickly. Also, the very small breeds are more susceptible to hypoglycemia (low blood sugar) although that would be more likey in puppies rather than adult dogs. Giving the sugar water was a good thing to try, but since it didn't make much difference, the symptoms you are seeing are probably not due to low blood sugar.
If this is something that has been going on for more than 12 hours or if she seems like she is getting worse (more lethargic, weaker) then it would be a good idea to have her checked out by a vet. I know we are going into the holiday weekend and that this may require a trip to the emergency clinic which will be more expensive, but because she is such a little dog , it is better to err on the side of safety and have her seen sooner rather than later. It is likely they will want to do some blood work and possibly take some x-rays so they can figure out better what is going on, and then get her started on the proper medication so she can get feeling better soon.
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I am concerned with the fact that you describe that the lethargy has progressed - if that hs occurred over the past 12 hours or so, be sure to keep a very close eye on him during the night - if it continues to worsen, he could get into a crisis situation before morning.
As I mentioned, the shivering can be caused by a variety of things and is not a specific sign of anything in particular - just one more "not feeling well" symptom.
I'm glad to hear you are planning to have him checked out in the morning - hopefully he will be okay until then, but do check on him during the night.