2 yr old small dog digestive problems

[johnsonm3012]

I have a 2 year old jack russel/chihuahua. He's generally a happy kid. Lately, he's been eating a lot of grass and throwing up constantly. We have 2 cats and the other day, he got into their kitty treats and tore apart the bag and then threw it all back up. He's been randomly throwing up a foam looking mucus with occasionally a little food in it. I noticed tonight that his neck is a little swollen on one side but not the other. He had an abnormally large BM earlier today and it was very soft. Normally it's more solid. Occasionally (past couple days) when he's lying down, and kids try to pick him up, he growls and may nip at them. nothing serious though. He also shivvers sometimes. I know I should be worried about this, but I'm not sure what to think because it's all so sudden.
I took him to the Veterinarian 2 days ago to get allergy medication because he itches a lot. His diet is Gold Seal (or something like that) and he seems to like it.

[PawsitivePet]

It's possible that the treats caused some lasting upset. I'm assuming prior to the treats he didn't have any issues?

Not to sound too graphic, but, what color was the poop? Lighter, yellowish, or a normal darker color?

Also, Gold Seal isn't a great food, you should probably consider finding something a bit higher quality - that may help the itchies, too. Maybe check out The Dog Food Project - How does your Dog Food Brand compare? to learn about food ingredients.

The growling and nipping may simply be because he isn't feeling well, but, don't allow it either way and make sure your kids do respect the fact that he isn't feeling well.