Sick Kitten? Need advice

I just adopted a male kitten. He is about 3.5-4 months old. He is neutered and had all of his shots. He was treated for internal parishes at the end of August and again on the beginning of September according to his medical records. But since being him home he has had had terrible foul smelling gas and his stool ranges between orangey brown and brown, sometimes soft enough he accidentally steps in it. And they smell terrible. I've owned cats before and I've never smelled anything like this. He also does this weird gag cough/swallow noise/thing all the time, where I think he is going to vomit but he doesn't. And what I think is is stomach makes girl if noises that just started tonight. Please help!

Internal parasites*

He needs to go to the vet.  He may need antibiotics.

okay, i made him an appointment for tomorrow. Thank you!

What are you feeding him?

wellness kitten formula 

It doesn't sound like a diet problem, unless he's allergic to something in the food.  The vet can advise you better.  You could try feeding him just boiled chicken and white rice to try to calm down his stomach until he goes to the vet.

He probably has a bacterial infection - possibly coccidia - and needs antibiotics. You can bring a stool sample to the vet in a baggie.