How is his weight doing as you can get him going on healthy eating and exercise thats the first thing, as he looses weight he will feel better. basket ball in your yard is good, walking, is good, soccer, gym ...Don't have foods in the house that he will be tempted by, let him come with you shopping and choose some healthy foods he likes . A lot of bullying does go on and maybe a talk with the teacher would help you find out if that is happening get the school involved in stopping the bullies .good luck