The first thing I would suggest is to change your brand of magnesium! The Mag-Ox you are taking is the type of magnesium with the lowest bio-availability: around 4% in some studies. In other words, most of the magnesium you are taking in pill form cannot be absorbed by your body. Magnesium oxide is the most common form of magnesium sold as supplements because it is cheap.
Magnesium
chloride is the form of magnesium that has the highest bio-availability. The one I take is from our local Sam's Club, but it is widely available. Just made sure that the ingredients label reads
magnesium chloride.
Here is an article about different forms of magnesium:
http://www.ancient-minerals.com/magnesium-supplements/