The color of the poo could be because all your baby has been eating is soy yogurt.
Curiously, what brand of soy yogurt are you giving?
How are you giving the soy yogurt? Through a syringe? How much of the yogurt is your baby eating?
Have you tried feeding your baby babyfood? Maybe just put a dab of it on your babies nose and hopefully it will lick it off.
You do have the reptisun 10.0 bulb now right? It is the tube bulb?
I assume you don't dust with calcium or multivitamin? Well when you can, you really should invest some money into at least getting the calcium. Babies really need it along with there uvb.
Flipping on the back is not a good sign, which is also why I ask about the soy yogurt. If there is an added vitamin A in it, you might want to consider stoping with the soy yogurt and just using baby food.
Sorry for the ton of questions, but I think they should be answered, especially since your beardie seems to have declined in health despite your best efforts.
-Brandon