constipation, loss of appetite, hairballs.. obstruction?

About a month ago we took our cat Lily to the vet because she seemed to be having trouble going to the bathroom. They did some x-rays and found out that she was very, very constipated. They gave her an enema (which didn't help) and some prescription food. She hated the prescription food at first, but I finally got her to start eating it and it seemed to make her constipation worse. When she went to the bathroom she would go a little bit but there would still be some left and it would be stuck in her anus. I stopped giving her the food and this stopped. At this point she's going poop once every day or every other day, but it's barely any. Maybe one or two small pieces, and she seems to really be straining. She also goes through these periods where she doesn't really want to eat for a day or so and eventually has a hairball. After the hairball she's fine and goes back to eating normally. She's almost 8 years old and has never really had hairballs. Maybe once or twice a year would she have one. I thought it was the new food that was causing it, and it seemed to stop when I stopped the food but she had another one this morning. I'm worried that she might have an obstruction or something.. I'm only 17 so I can't take her to the vet by myself. But my parents are convinced that she is fine and won't take her back. What should I do?? I'm really worried about her. 

If she will wet food I would give her wet food to increase her fluid intake.  The prescription foods have added fiber which is hit or miss.  It does help some kitties and makes things worse for others.  I would also try Miralax, it's a human OTC medication.  It's labeled as a laxative but it works by drawing more water into the colon.  It's a tasteless powder and can be mixed with wet food.  Start with 1/8 teaspoon twice a day and adjust the dosage to find the right one.  It seems a little expensive but it comes in a fairly large container that will last a long time for a kitty.  At least the large container was all that was available at the supermarket I go to the last time I looked. 

A lot of kitties have issues like this during shedding season.  It is very rare for a kitty to become obstructed from hair but they can feel really bad from the hair they are swallowing.  Do you free feed?  There is some evidence that free feeding makes things worse.  The last thing to leave the stomach is undigestable things like hair.  When the kitty is getting hungry from an empty stomach the spasms in the digestive system get stronger and push the hair out of the stomach.  With free feeding this doesn't happen and it builds up in the stomach.

I agree with everything Denise has said.  And when cats are constipated, they don't want to eat.  Believe me, I've had a chronically constipated cat, so I know if what I speak.  The only thing that finally helped my cat was putting him on a twice a day dose of a generic Miralax (less expensive ).  Since my guy didn't really like canned food much, I would mix just 1/8 teaspoon of the Miralax into a teeny bit of water, then mix that into just a teeny bit of gravy from some canned food, just enough for him to lick it up.  Most cats who don't eat canned food will at least lick the gravy.  That way I made sure he got his dose and we didn't have to stress him out by giving it to him via syringe.  And when I say a teeny bit of food, I mean the total amount in his bowl couldn't have been more than a teaspoon!  After he ate that, then he got his regular food.

BTW, IF you are already feeding wet food, then you've got it made .  The Miralax (and generic stuff IS totally tasteless and does NOT gel up like most laxatives, so it's just like adding a little water. And speaking of adding water, most constipated prone cats need more water, so it's a good idea to add more water to her wet food if she'll take it that way..  And you can also try to add in a little canned pumpkin too, for fiber.  It's a good type of fiber that sholdn't bulk her stools.  Some cats don't mind the taste at all.  Use pureed pumpkin, not pumpkin pie mix.  About 1 Tablespoon per day, spread out over her meals.  Just mix it into her wet food.

And if she's tossing up hairballs, be sure to brush or comb her frequently to help minimize the hairballs.