Fatigue and facial tingling?

This is related to something that I've had since I was a kid, its something that I've been aware of but never been able to pin down. I'll often have times throughout the day have my mental energy hit a wall. Standard response is that's normal, it happens to everyone. I worry though because it seems to impact my functioning and hit perhaps thicker for myself than most people I know. As of my early 20's especially forcing myself through it, I often get to the point where my forehead will start tingling from this situation - it's happened more and more often, as far as I can tell its the result of pushing myself farther than I should be going and this sensation typically goes away with rest. The real problem is that on some days I can get this point simply from reading a few paragraphs, other times when I need to lay down and close my eyes I'll feel like I'm expending more mental energy just being conscious than I have to budget. Needless to say when this does happen it impacts my work performance significantly, some days being better or worse than others. Occasionally in the past several years I've had times where this tingling would wrap my entire head, typically on these days I felt completely spent - like I could barely think about anything from start to finish. A bit more background on my health - I was diagnosed PDD-NOS when I was 11, I do have autistic traits although they aren't nearly as outward as they once were. I'm currently 31, the only other health considerations I have are hiatal hernia (maintained with Prilosec), I've also had life long sleep issues for which I take melatonin on a regular basis, I average 6 1/2 to 7 hours of sleep per night.

I find myself often wondering at this point what this is a sign of: whether I have an additional health issue that's gone undiagnosed (I talk to other people with Asperger's/PDD-NOS/autism on this - few can relate) or if perhaps if I've just stretched myself passed what my nervous system can deliver? I'm trying to figure out where to go with this as I realize that I'm at a point where I need to make a decision going forward on this - either in regard to medical attention or change of lifestyle if its something that can't be resolved.

My question, if this is unlikely to be something that stems directly from my previous diagnosis, where would I want to look first to get this looked at further? If this is an autism related issue is there any medicine, supplement, or set of general health practices that helps to reduce this effect?