If it were me I would stay away from the wheat grass. I've read a lot of people who react to it and it's probably best to just go with what you know is gluten free and continue getting yourself healthy.
Have you looked into working with a colon therapist? I have been working with one for 8 months now and the therapy has completely changed my life. I recommend this 1000%. Keep up with the juicing. From what I understand apples and lemons are excellent for the colon. Also cucumber, carrots, beets, radishes, parsley, celery, dandelion, ginger, garlic. Along with all the other wonderful veggies out there. I've been juicing on and off for a few months now but really started to get into it. I've been reminded several times to make sure that I'm adding extra fiber to my diet. Juicing alone is not enough.
I too live with a very strict food program. I get protein from seeds and beans: hemp seed is awesome (doesn't taste like anything and you can sprinkle it on everything), flax seed (you can ground it up and add to your juices), sunflower seed, pumpkin seed. I make lots of hummus and different bean dips to eat with fresh veggies. You can make all different flavours.
For me... exercise was a big part of healing. I got a membership to the YMCA and do aquafit 3 to 4 times a week. Keeps my energy and spirit up to keep me on track with my food program. I also found that working in the pool was much easier on me physically. With colon issues I was finding it hard to do any sort of running/aerobics. But with swimming I have no issues.
Good luck to you
Keep up your hard work. It will pay off