Thanks everyone for your input, much appreciated!

Citric acid is in everything!!!

It's making an already limited diet sooo much more limited, YIKES! The website you found Scarlett's mom is great, thanks! I have printed off the list of foods containing citric acid and have stuck it on the fridge.
Funny you mention cranberries RachelC. After 5 days, DS is only just getting over the worst flare-up he has had thus far and I have been wondering if it was the cranberry sauce I ate Sun-Tues (left overs!). It's either that or eggs, I don't know.