Well, your substrate should never be damp for more than a day...

Ara, you are correct, the lamps are what is decreasing your humidity. My best suggestion is to get a reptile thermostat and a UTH and ditch one or both of the lamps. You will never have an issue with humidity after that.

How are you measuring humidity? What kind of hygrometer? If it isn't digital, I recommend getting a digital one so you can get a more accurate reading. Those dial ones don't really work.

If your snake is an adult, 4 weeks is not a long time to go without eating. Has this snake eaten for you at all yet?