Cat Sickness

Question
I recently put my 23 pound cat on a urinary tract cat food.  She has lost about ten pounds and her tract health has greatly improved.  The problem has been that she constantly is throwing up her food.  She used to only throw up when she would eat way too much food.  Now she will throw up her food about 3-4 times a day. On the other food (Iams reduced fat food) she had a lot of tract problems and would go poop on the floor beside the litter box a lot.  Now she no longer does that.  I have been giving her NutroMax Urinary Tract Health food.  We also recently moved and now have well water as opposed to city.  Could this be causing her problem with throwing up?  Or is it the food?  Or is it something entirely different?  She really freaks out and urinates all over when I take her in the car so I have been relunctant to take her to the vet.  She seems to be happy other than that.  She is about 10 years old.  Any help would be appreciated.  

Answer
You need to take her to the vet and get some blood tests.  It is very hard to get cats to lose weight and 10 pounds in a cat is almost 50% of her body weight; therefore, I would be concerned that there is an underlying medical problem such as diabetes or thyroid disease that is leading to the vomiting and such drastic weight loss.