I'll get back to your other questions later...I'm racing out the door. But wanted to address the digestive enzyme issue...does the formula you are using contain HCL (hydrochloric acid)...it sounds like it might. Some do and some don't. This is the same acid that resides in your stomach. Many people do well with it, but some already have plenty and react with burning and acid reflux when they take extra.
If your formula does not contain HCL, I would suspect that it was something other than the enzymes...unless the formula contains added ingredients or has fillers in it that you might be reacting to. Digestive enzymes are present in the body naturally and also in foods. They are essential for digestion and most people are lacking in sufficient enzymes unless they're on a raw food diet.
Could you possibly have caught a bug or eaten something that didn't agree with you?