The eating grass and vomiting clear liquid are related. Dogs have a natural instinct to eat grass when they are nauseous. Sometimes the symptom is caused by a simple sensitivity to their own stomach acidity, especially when the stomach is empty. We see this the most with dogs who are fed once a day and/or are fed a premium, high-quality, meat based diet that doesn't stay in the stomach for very long. Increased feedings, increased fiber content of food, or giving Pepcid AC are all good ways to combat this type of vomit.
However, nausea and vomiting can also be caused by about 100 different metabolic problems. With a history of anesthesia recently, I would want to be sure the liver and kidneys are very healthy by checking a blood panel. Although modern anesthetic drugs are quite safe, sometimes the stress of a procedure, blood pressure changes during the anesthesia, or the drugs themselves can take a patient who is borderline with organ finction and push them into problems. The earlier these are detected, the easier and better treatment will be.
I suspect the shaking is a result of the nausea as well. However, some metabolic problems can lead to electrolyte imbalances that cause shaking.
Sorry for the ramble. In short, the problem is likely innocent that can be addressed through diet and/or Pepcid. However, I think it is well worth a laboratory panel to be sure that's all there is.
Good luck.
This post provides general information only and should not be used to diagnose specific patients. All treatment decisions should be made in conjunction with a veterinarian after thorough examination.