my bearded dragon has had stress marks since i got her (17 days ago).. i'm not sure if it's still stress from her settling in, but she seems to be nicely settled... so i'm not sure what could be causing them...
The two things I would check for first would be the temperature under the basking side and the cool side. and also if you have your dragon in an aquarium, then they may be seeing their own reflection in the glass which could be causing stress due to the fact that they think they might be in another dragons territory (is that how you spell it, sry its late here). Check both these things and post what you know on here. Hope thats helps.