My cornish rex

We purchased a cornish rex she is almost 5 mths old, since we got she has had softish stools that are yellish/orange in color, it smells awful and she farts awful all day and seems bloated, she has been to the vet, she has had her stool sent to a lab and tested she is free of parasites. The vet gave me script for vet approved high fiber food and its been 3 weeks and its not getting better in fact it seems worse, she now poops 3-4 times a day instead of once. Other then that she is happy, playful and active. I just put a call into the vet because this is getting ridiculous, every site I am on said it should be solid, and brown kinda like a tootsie roll and hers is nothing like that. Any suggestions?

Did she have the gas and the lighter, more frequent stools before the prescription food??  I'm wondering about what she is eating if the vet has thoroughly tested her and can't find any "invaders"   I've also had added-fiber diets the vet recommended backfire in my cat and things go the other direction than what we wanted.

Calling in somebody much smarter about food issues than me-  @missmimz  can you help her?

Yes she has had it since she came home, the vet changed her today to Purina En, to see if that helps. Hoping something helps. Our vet sent the stool to a lab to be tested and everything came back negative. I was wondering if maybe she had some bacteria overgrowth in her tummy and needed some probiotics or a round of antibiotics?

What have you been feeding her? Kittens have very sensitive digestive systems and get diarrhea very easily. I would suggest feeding a high quality wet food only diet. Personally, I'm not a fan of an RX foods as I don't think they are biologically appropriate for carnivores, nor are they worth the money. You can achieve the same, or better results most of the time by feeding high quality food. I'd also suggest giving her a probiotic. When my kittens were young they all would get diarrhea at random points. I started adding nexabiotics to their food twice a day. It is a human grade probiotic, but it's safe for cats and kittens. Kittens just take a smaller dosage. Here's more info about it. You should of course, discuss this with your vet if you decide to use probiotics, however, they don't interact with any medications and again, are safe. 

Here's a list of wet foods I like. Not on the list, but a food I also like a lot is Feline Naturals new canned food. Merrick LID is also decent too, and available at Petco.

http://www.naturalcatcareblog.com/2010/12/the-7-best-natural-commercial-cat-foods-so-far/

Here's some info about probiotics

http://www.foodfurlife.com/my-cat-has-diarrhea---what-do-i-do.html

http://www.foodfurlife.com/use-probiotics-in-cats.html