Back in high school, you were one of the top few students. So you could take a massively ambitious set of classes and still do well. Maybe you were also doing theater and a sport. When you arrive at college, there's no way to predict how heavy a load will really work, since your classes are now harder. You might be trying to do too much.
If your workload is cutting into your sleep, you definitely have a load issue. You cannot do technical work on insufficient sleep. The same applies if you are eating poorly, e.g. grabbing quick junk food rather than having proper meals.
College is not a race. It's important to take the right load and do well at what you attempt. You don't gain much by finishing early or accumulating extra credits.
If this sounds like your situation, you need to lighten your load. Drop a class or reduce your outside activities. Speak to your advisor if you aren't sure which class is safe to drop. Avoid ending up with a schedule that consists entirely of technical classes: Gen Eds and outside activities help you escape and stay sane.
Many medical conditions (including minor ones) can cause fatigue. If there is any chance of this, speak to the folks at McKinley.