Stuck shed (possibly eyecap) or dehydrated snake. Either way, your temps and humidity are likely off. Are you still using those stick-on dial thermometers and hygrometers that you probably got at the pet store? And if so, are they still stuck to the side glass toward the top of the tank?

If so, that's possibly part of the problem. The analog dials can be very inaccurate, and you should be measuring the temps on the floor of the enclosure where your snake is actually being exposed to the temps. Also, if you haven't already done something to help hold humidity in that tank, you should look into screen lid mods that can help increase humidity. You can use foil or plexiglass to cover 2/3 of the screen lid to help hold in any humidity that isn't being baked out of the air with the lamp...