Could worms make that happen? He seems really skinny...I've been feeding him like 4 cups of food a day (I increased it recently cause he seems too skinny to me...) How much do you feed you dogs (large dogs around 60 lbs)

Edit: I just read that worms can cause vomiting, diarrhea, etc. He also has diarrhea sometimes...not always though. He licks the fur/skin off the sides of his belly....I wonder if all this could be worms? I think I will check with my vet.