That thermometer is only reading the temperature of the air around the glass. And even then, it's not very accurate. The dial thermometers have been proven to be wildly inaccurate. Plus, they do not have the ability to show you the most important temperature you need, the basking surface temperature. Luckily, you can pick up a good digital thermometer with probe end for less than 5 bucks on amazon, and less than 10 bucks at a local petstore. You need to get one, as knowing your basking surface temperature is one of the most important aspects of a dragons health.
Second most important would be proper UV. Two things typically cause all of the symptoms you are describing. And that is 1, improper temperatures. And 2, improper UV. And sometimes it's a mixture of both.
What are you currently using for a UV bulb? Is it one of the coil (CFL) type bulbs?
-Brandon