First thing I would do, is check your tempertures with the lethargic dragon. Make sure you basking areas are between 95-115F, air temp around 80-90F and cool end between 70-80F. Next, if it hasn't been done recently, change your UVB bulb if it's more than 6 months old. Also make sure the light intensity of the tank is high, if the lights are all dim even if proper heat is maintained, dragons can go into brumation thinking its time for that.
If the dragon isn't eating at all, make sure he's well hydrated, luke warm baths help with this.
As the other poster asked, did your reptile vet run fecals (examination of the dragon's poo?). Did he do any bloodwork or x-rays?
For the other dragon with bloody stool, is there alot of blood, or just a trace? Also, are these dragons housed together and what sex are they? Dragons who have recently mated can sometimes pass some blood though this should go away after a couple poops, or even just one. Also, what are you feeding them? Bright red vegetables, flowers or dyed pellets can cause red staining of the stool.
Below are a couple links to qualified herp vets, if you haven't see them before, might be a good ideal to go through them and see if there is another vet in your area with more experience with herps.
www.herpvetconnection.com/
www.anapsid.org/vets/
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PHLdyPayne