I've spoke with several people who felt that plain glutamine was helpful at first, but with continued use found it not good for them. I suspect that it may have to do with the ammonia released in the intestines when glutamine is ingested.
Instead of glutamine, I'd suggest you try a mixture of glutamine and alpha ketoglutaric acid called Perque Endura Guard. The combination recycles the glutamine, making it more effective. Also, the alpha ketoglutaric acid will help your body deal with the ammonia released from the glutamine.
Realize that glutamine could make constipation worse. Even this Perque Endura Guard combination may be a problem for constipation. It may be helpful though, if you suffer from diarrhea.