I really think you should consult a vet about this as it is not advisable to give animals human medication. Hope your puppy gets well soon.
You call your/a vet asap. If your pup is unable to go to the bathroom it isn't a good thing and can be serious. It could be something like intestinal blockage (pups eat lots of things they aren't supposed to) which needs a veterinarian. It may be something minor but not worth the risk (and higher bills) of waiting. The shaking probably means your pup is in pain due to whatever else is going on. I hope it's nothing much and your baby is feeling better very soon.
www.americanshihtzuclub.org
www.americanshihtzuclub.org
I think you should take your puppy to the vets.