Well I read your plea in the off-topic section of the board, and although I have no experience in fish illnesses, I thought I would do my part to research the symptoms you've described and come up with something to share.
Several other forums I went to suggested that white stringy poop meant internal worms, which I think has already been concluded here. As far as medication goes, a vet on Ultimate Bettas recommended Paracide-D and DeLos from National Fish Pharmacy, and included a link: http://www.fishyfarmacy.com/products3.html#Paracide-D
You can view the original thread I just summarized here: http://www.ultimatebettas.com/index.php?showtopic=24803
I don't know how helpful this is, or if camallanus worms are your problem, but the symptoms appear related to yours so there might be some valuable information?