I'm glad to see that you may have finally found your problem and hopefully a solution. I posted how lead poisoning can cause candida here: //www.curezone.org/forums/fm.asp?i=1797653#i
I bet your severe reactions calm down after a few chelation treatments as they will hopefully relieve some of the burden on your liver.
I would not assume you are not still getting contamination unless you know for sure why you have lead exposure. My unprovoked lead levels were very low but high after a challenge. I found out my bathtub was lead glaze that was exposing me badly.
It's good to check your bathtub, water supply and any ceramics to see if you can find the source of exposure. Or did you have a job in the past that might have exposed you to lead?