Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this constipation problem with Tom although it's a fairly commonly seen problem in many cats as they age.
Many cats who can't defecate will stop eating and may start to vomit so his other symptoms could be consistent with this primary issue
However, having said that, cats who can't urinate can also behave this way. If there's any question in your mind as to whether he's trying to defecate or urinate, then a vet visit sooner rather than later may be prudent. Cats who can't urinate are considered a medical emergency as you might expect.
But, if he's been urinating and you're fairly certain that he's straining to produce stool, then I do have a few suggestions which may be of help. While many cats who are badly constipated will need enemas given by a vet, there is an over the counter option which you might consider.
1. Pediatric glycerin suppositories can be used in cats but you'll want to double check the label; those with phosphate can be fatal to cats. http://pedia-lax.com/products/liquid-glycerin-suppositories
You may need to administer several over several hours if he's badly constipated.
2. Warm water enemas can also be given although this is frequently very difficult to do in a cat by the pet owner. Basically, it involves use of a lubricated (with K/Y or Vaseline) syringe or small turkey baster gently inserted into the rectum and the contents squirted in to the colon. It usually takes quite a few enemas to loosen up hard stool.
3. Hopefully, he's able to defecate on his own within a short period of time. If that's the case, then use of oral laxatives may be given to help prevent another episode. Feeding canned versus dry food is also encouraged.
a. Over the counter hairball laxatives such as Laxatone or Laxaire which are brand names but every pet or grain store will carry these products. I usually suggest 1-2 inches 2-3 times a day.
b. Canned pumpkin (NOT the pie mix) at a dose of 1/4-1/2 tsp per day.
c. Over the counter, human Miralax (polylethylene glycol 3350 aka macrogol 3350) at a dose of 1/8th-1/4th tsp daily which can be increased until soft stools are produced.
If you're unsuccessful in getting Tom to defecate on his own and/or he continues to vomit and/or doesn't want to eat, then I might have him seen.
I hope this helps and provides options for you to consider. Deb
PS. I see that you submitted this exact same question and requested an expert who isn't currently online. If you access this question, you might want to contact Customer Service to close the other one (so that you don't get charged twice).
Just an update: I was able to contact Customer Service who closed your other question.