Please make sure that your doctor is checking your RBC magnesium. Doctors will usually check serum magnesium which is where 1% of your magnesium store is and does not reflect true magnesium levels. Check the link below.
http://www.ncbi.nlm.nih.gov/pubmed/20170394 Also, most magnesium supplements on the market have a very low absorption rate. One of the fastest ways to get the magnesium into your cells where it is needed is to use magnesium oil spray (not an oil) and follow the directions on the bottle. It can cause a little itching from the salts but you can wash it off after 20-30 minutes. I stopped heart palps and leg cramps within 5 minutes with magnesium oil. It does take a while to restore you magnesium levels to optimum levels. You can find magnesium oil in health food stores and online. Also, diet is number a priority. sugar and carbonated drinks are some of the foods that deplete magnesium.