My 44 Year Old Son Recently Had A Hole In

My 44 year old son recently had a hole in his colon and had surgery 3 weeks ago which resulted in a temporary colostomy which will be reversed in 3-6 months. The cause of the hole was diverticulitis. Anyhow, he is very weak and has lost his appetite. He is down to 175 pounds from about 200. Is this loss of appetite common? How long is the usual recovery period so that he is not so exhausted?