Have you done a fecal, it will show some worm issues but encysted strongyles do not show in a fecal. A big belly is a sign. My vet had me do a Panacur Equine Guard 5 day treatment. I had to worm twice with different products 3 weeks apart. Ask your vet. Have her teach checked again maybe something was missed. If all this fails, I would have the vet do blood work.