Im very worried about my dog Spanners

I think the little guy has bulimia

Get this, for the last week or so, everytime he eats, a little while later, he goes outside, eats a trailerload full of grass and sicks up his dinner everywhere!

Ive tried varying his food, from dog nuts, tinned dog food, even proper meals and prepare him a portion of what im preparing to have for a meal. Makes no difference. He'll eat everything no problem and seems to enjoy it and then same story again, off out, generous helping of grass and puke puke puke

He seems pretty happy otherwise and is full of life so im stumped

Does my dog have issues with his weight, maybe not proud of his body, body image problems?

Please help!