Maybe this could be related to the famous 'runner's runs'? I just read an article regarding a study where they found that probiotics helped with those sorts of symptoms.
I've noticed myself that I sometimes have soft stools when I've had an intense workout, and wondered if it could be related to the above mentioned runner's problem - and recently increased...
Next Protein's Designer Whey is Gluten Free, and states is on the label - it's not too expensive, either (especially in the 5 pound size). I order it online, since I haven't been able to find a better deal locally - although I did see that there's a brand at Bigg's called Jay Robb (sp?) that's reasonable and gluten-free.