A couple of comments here..and I'm not a Dendrobium grower so take them with a grain of salt.
Was your plant exposed to temperatures below 55? These need to be kept warm.
Dendrobium generally like to be pot bound … repotting while it's blooming is sort of stressful ( even if it was in the wrong mix to begin with). I would cut the flower spikes and enjoy them in a vase. This will allow the plant to focus on new roots.
Hold off on fertilizing until you see new roots.. it's kind of like asking you to eat a big meal after surgery.
If the leaves were green when you got it, odds are it's reacting to a change in its situation.
Fingers crossed that it settles down soon for you.
