When you find a place to do the fecal test, ask them how fresh it needs to be and any special instructions in bringing it to them.
Maybe you could try a different kind of grass hay, or even mix in a little alfalfa if he likes it, to hopefully get him more interested in eating the grass. Alfalfa does have to be gradually introduced, so just start off with a small amount. If he's not eating very much hay, that could be the reason he keeps getting the small poops. He needs the fiber from the hay. If all else fails to get him eating hay, you can sometimes find large bags of plain timothy hay feed pellets(used for horses) at feed stores. I had to do that for one of my new rabbits that wasn't used to eating hay, just wouldn't eat it. But he would eat the hay pellets, and gradually he started nibbling on hay and eating more and more, so that now he eats a normal amount. Sometimes you just have to try a bunch of things before you find something that works. just keep an eye on his weight, since he's not getting very many pellets right now and not eating very much hay, he may not be getting enough to maintain his weight. If you start giving a little alfalfa, that should help though.