Hello, and welcome.
I'm so sorry Forrest Gump is experiencing this problem. Try offering him some plain cow's milk (1 oz.). This is a natural laxative for most cats, as they are lactose intolerant. You can offer him some hairball remedy like Petromalt or Laxatone to lick from your finger. If he won't do that, put a ribbon of it down on his forepaw, near his paw, and he will lick it off as cats hate 'sticky' on their fur.
You can also mix 1 tsp. of plain, canned pure pumpkin (not pie filling) into a small amount of his wet food, every 12 hours; this contains natural fiber. You can add, instead of the canned pumpkin, baby food stage 1 pumpkin or sweet potato containing no other ingredients. Give 1 TBS. once a day.
You can sprinkle 1/8th of a tsp. of Metamucil into a small amount of his wet food.
Choose only one of these to do, but, you can use the hairball remedy with any of them, just not simultaneously.
You can take a lubricated rectal thermometer (with plain Vaseline or KY Jelly) and put it in his anus about 1/2 and inch and rotate it, then remove. This may stimulate a bowel movement, but be very careful.
Continue to keep him well hydrated--you can add some water to his wet food and in addition to water, you can add tuna water from a can of tuna.
Do not feed any dry food.
If there's still no movement, keep in touch with your vet and ask if the feces may need to be removed surgically, if nothing else is working.
I hope Forrest Gump is feeling much better very soon.
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