My poppy vomits or regurgitates, don't know for sure which is which. Every couple of days it seems he gets in this convulsion state and brings up what looks like yellow/whitish liquid. He likes to roam around in our backyard quite a bit, is it possible something that he is eating out there that could cause this to happen? If not, what could it be?

If he is only vomiting a yellowish liquid, that sounds like the lining of the stomach, simply meaning the food he has eaten is digested and that is what is in the stomach.

It is possible he is eating something causing an upset, but normally he would vomit back up something that has not been entirely digested.

There are many reasons a dog may do this, and a vet will be the one to give you a definitive answer. I would not even want to take a stab at guessing the various types of things that could cause a puppy to vomit. To numerous.

My mom's poodle did that...pancreatitis from feeding too much human food. The dog almost died twice before my mom quit feeding her table scraps.

Ulcers can produce this, but since the dog is young, I wouldn't suspect that as a cause. Yellow foamy stuff is often just bile. He may just have an empty tummy. If has has gnawed on some grass, he will likely regurgitate - that's why they eat grass. I do not know what breed of pup you have nor his size, but if he is in that rapid growing phase, he may just need an extra feeding to compensate for all the calories he is burning off romping in your yard.