I would recommend taking this w. dragon to the vets if this continues. it wouldn't be a bad idea to check for parasites anyhow.
I assume that you got the mite spray because he had mites? Is it one that is made for reptiles? (I have never had to use a mite spray. I did have a w. dragon that had a mite but it was the kind that burrow under the skin and it was given a shot to get rid of it.) How often are you spraying him? Some mite sprays can be harmful to reptiles.
How big/old is this water dragon?
You said that you got calcium....what kind? Did he eat at all since you have had him? What foods/insects have you offered him? Do you gutload his insects? Do you dust with minerals/vitamins or calcium/D3 supplements if he's not getting any direct sunlight?
If he is over 6 months of age, do you offer him any greens (dandelion greens, kale, collards, mustard greens, ROMAINE lettuce, endive, etc.), fruits (apple, pear, melon, berries, kiwi, etc.) or veggies (diced carrots, sweet potato, sweet red peppers, squash, etc.)?
You said..."i have basking uv and uth for night time heating"...I have never used a UTH....but my w. dragons' cage temperatures never go below 70F at night. I assume that there is no glass or plastic between the UV light and the dragon? Your cage temperature should be in the high 70's to low 80'sF and the basking area can be in the high 80'sF.