My thinking: I don't know why people take it in oil, in traditional thought this is never used. Why not take the tablet form?
Magnesium is a tricky mineral in that it works with other minerals. Calcium is antagonised by magnesium so it is possible that you are having a calcium deficiency as well. Typically people are higher in calcium and low in magnesium. You could be deficienbt in both. Try a high quality calcium supp.
It is possible that you are antagonizing potassium as well. But I would try the calcium first.
A test that can take out some of the questions would be traceelements.com, worth every penny.