Kitten keeps vomiting

Question
This could possibly be a long question so i do apologize.

I work in a Veterinary surgery as a Kennel Nurse, about 4 weeks ago we had a stray kitten brought in, which i am fostering ( well keeping i should say, we have been through so much i wont let her go). We estimate her age now is approx 8/9wks.

We were feeding her Cimicat for the first couple of weeks, then we changed her onto solid food.

First we tried her on Hills i/d, but she was vomiting after meals. I then tried her on Hills Scienceplan Kitten food. But she continued to vomit. So i put her back onto milk, to build her strength up. We decided to X-Ray her at work to check for problems, we gave her some barium liquid and did approx 4-5 X-Rays. The Vets at my work looked at the X-Rays and were able to rule out megaesophagus, Persistent Right Aortic Arch and pyloric stenosis.

So we put it down to her having a sensitive tummy, however

She is still vomiting !!

She is currently on Whiskers Kitten food (wet), we thought the Hills kitten might be a little rich for her.

I have tried her on many diff flavors incase she had an allergy to chicken (which i know is un-common in young animals)

What is puzzling me more than anything is that her vomiting isn't consistent.

For example, today and yesterday she was sick about 3 times on each day. The previous couple of days she was only sick about once each day.

I have tried giving her zantac liquid incase she had a bit of reflux but i am really stumped as to what is wrong with her.

She was weighed last week and was 600 grams. She is lively and energetic and her stools are normal. She normally has one poo a day which is solid.

She has been wormed also.

If you have any advice i would truly appreciate it

Thank you for taking the time to read this.  

Answer
For starters I would take her to another veterinarian if the one you work for can not solve it.  I myself am not a veterinarian so I can not give you a list of things it could possibly be.  If the kitten is expending more energy than it is processing, due to regular vomiting, she will eventually become dehydrated, go into organ system failure and die.  

For food I would suggest an all natural brand like Innova, and if that fails to work within 5 days I would find a specialist.  States with a veterinary school have experts available and have reasonable fees.

My personal cat had something like this once, and the vet couldn't figure it out until he opened her up.  It turned out she had a punctured intestine and food couldn't get through.  It was not something visible on X-rays.  

Please let me know if there is anything else I can do for you and how the situation turns out.