What causes MS-related fatigue to be so severe that it affects thinking, coordination, speech, and even the ability to sleep?

Fatigue messes with my whole life. I am not able to stay awake but I am also not able to sleep. I feel like I am in the constant state of grogginess. I have poor thought processing, memory, word recall, and coordination. I barely leave the house because I look like I’m on drugs when I go out in public. Anytime I get the least bit still I fall into the half awake half asleep state I live in because I can’t sleep and I can’t stay awake. I take pills to stay awake and pills to sleep and neither one of them work! I am at a loss as to what to do.