First off before looking at diseases, I'd make sure you were
getting enough magnesium. This mineral is often low in Americans.

I have a thread here that explains how to supplement with it successfully.

Twitching in the body can be due to electrolyte problems.

And then the second most likely is a blood sugar problem.
When blood sugars go down, twitching is very common.
When people are pre-diabetic, or beginning diabetic, weakness is one of the first signs.
Insulin resistance is very common after the age of 40. But some folks are showing it now in their 30's. In fact some kids in the teen years are coming up type II diabetic today.
This is best evaluated with a 3 hr glucose tolerance test.
You can also have a fasting insulin level drawn, as well as a fasting glucose to start. If the fasting INSULIN level is elevated then insulin resistance is present.