Argh, that's so frustrating!! I can't beleive you ladies don't get better support than that.
So, if it's the Alimentum, I don't think you'll be able to tell within one night. Traces of things can take up to a couple weeks to get out of the system. Could you add in a cluster BF somewhere in the late afternoon, early evening if you think he's still hungry? But, on the other hand, if he tolerated it well before, I don't think it would change.
I just didn't want to totally rule that out as being a cause, as it seemed to coincide with the NW.
However, I didn't remember you mentioning oatmeal before. Oatmeal can definitely be binding. How long has he been having that? I think sbchich's advice is really helpful and would definitely give it a try. I can understand how you feel about juice, but actually after reading that, I remembered that my SIL had to do that with my oldest niece as well, and she is by no means a juice or sugar addict today (12 yr old).