first: pet stores and their employees are terrible sources for information. i would not rely on the average pet store employee for advice or knowledge unless i was proven otherwise.
it sounds to me like the snake might not be comfortable with your husbandry. what type of thermometers/hygrometers are you using? what is your temperature and humidity at currently? what is the temperature of the enclosure floor above the heat pad? is the UTH (under tank heater (heat pad)) connected to a thermoSTAT?? ALL heat sources MUST be regulated by a thermoSTAT or a lamp dimmer/rheostat. if the UTH is not regulated, PLEASE unplug it until you can get a thermostat or rheostat (a thermostat is far superior to a rheostat which should only be used in a room with a consistant temp). a UTH can reach 140° easily and burn/possibly kill the snake.
please read through this enclosure set-up guide and make sure you have everything you need and that it is set up correctly. once you do that you should see a change in the behavior.