Problem with veggie juices

Hi,

I have posted before having trouble with vegetable juices but didn't get satisfying answers...
Now I am trying slowly to experiment and it is not going well...
For some reason my stomack feels ill when I drink certain kind of juices, like anything with beets, garlic or collard greens.
Today I tried my first wheat grass juice, I put maybe an ounce or two in a big cup of apple juice (freshly pressed), I put water in it to dilute it, I tried to sip it really slowly - and the same thing happened, my stomack was not feeling well, like I ate something bad, almost pain-like, sometimes I even question myself if I had the pain in my stomack, maybe it was my liver (I'll try my 3rd liver cleanse this weekend, just in case. :) )... Really weird feeling.
I would love to go on some kind of fast but with my Candida my only choice could be veggie juices - and here we go...
Can anyone help me to figure out what is going on?
Thanks a lot.