Karla gave you good advice. You need to switch to an appropriate diet and they do sell formulas for weight control. You should feed twice a day and don't give any extra treats or table scraps, etc. Try feeding raw carrot or veggies for treats.
There is an off chance this may be a thyroid problem. Your Vet can check that with a blood test.
If your dog is unuse to exercise, you need to build up slowly.....Do not expect him to have alot of endurance in the beginning....Start slow and build up gradually...
If you are feeding him a low quality food, this may be part of him problem....If what he eats is full of grains, by-products, chemical preservatives, dyes & no real nutrition, you need to adjust to a high quality food...All the grains in most dog foods are very fattening....
Also, you can add fresh veggies to his meals & gradually start cutting back on his food....This will help keep him full w/lower calories....
Be patient & don't give up....The change should be gradual for longterm benefits.....Good luck & let us know how he's doing.....Karla
A dog (exspecially one who is over weight) should get at the at least 30 minutes of some type excersise a day. Have you started feeding it the weight control dog food as well? This will help the dog help lose and maintain a healthy weight. If it continues to be overweight it could cause damage and health problems for the dog in the long run.
Good luck with the pup!