Constipation?

I have a two year old walker that seems to be bloated and constipated. He hasn't eaten to much food for a couple days just kinda nibbles at it, and he's not one to pass up food haha. He's a little chunky but he looks like hes 20 pounds over weight. He's been sleepin most of the time to. Just doesn't act normal. Anybody else have this problem or have any remedies to maybe help out this problem?

Cod liver oil......and stand back....lol....try switching feed to a feed with a high fiber.....not all dogs do good on same food........Might have to try a couple different brands to find something that agrees with him......Another big factor is water consumption......with cold weather coming on us water is important......his/her bowel impact might not be getting enough moisture in him/her too.....Cod liver oil will loosen the stool and provide essential vitamins and minerals that with the oil should help,but high fiber is key.......