Fecal impaction

Hello, my 4 year-old-male cat had not passed any stools a few days ago, so I brought him to the vet yesterday. I told her that he probably had fecal impaction since the stools that came out when I bathed him were quite hard despite being a sort of browny yellow. After doing some X-rays, she agreed that he was severely impacted, and probably for a week or two. She supposedly did an enema of the portion closest to his anus, but my cat is still not pooping: he made only one small one this morning and urinated a little. 

I did everything that was recommended by feeding him W/d and giving him a bit of canned pumpkin mixed with some of his other wet food. One problem I seem to be having is getting him to drink water.

He still seems very lethargic. I am not sure what to do.  I've already spent close to $500 and can't afford to spend another similar sum. What I find odd is that even though he was said to be severely impacted, how could the vet have gotten rid of most of the poop (she says there is still a bit left) in a very short amount of time? He was only there for about 2 hours. I'm afraid that there may still be a great deal left judging from the way he is acting.

Anyway, I'm at my wit's end. I would like to hear from anyone who has had similar experiences w/ fecal impaction.

If he is lethargic, you have to go to the vet - a lethargic cat is NEVER good.
Will he eat canned food? If so, stop the dry food and immediatelly put him on a 100% canned food - that will take care keeping him properly hydrated.
Also, you can give him Miralax - if this is an adult cat, 1/4 TSP a day. For a severely constipated cat, you can give that dose twice a day for the first few days.
You can keep him on Miralax indefinitely, it is very safe for cats, and it is a good stool softener..... Just keep him on the lower 1/4 TSP/day dosage.
The best thing to do for him though, is to remove him from dry food, put him on a wet diet.....
And again, if he is lethargic - take him to the vet PRONTO.

Thanks, Carolina--fortunately, he was eating quite a bit yesterday. At the moment, he is primarily getting wet food, mostly W/D mixed with a bit of Fancy Feast.

Today, he finally pooped and urinated plentifully. But he still seems kind of lethargic so I will call the vet.