I disagree with Robli's answer. It is extremely unlikely that you could overdose on magnesium oil. Also her recommendation of twice as much calcium as magnesium is not really correct, although it is seen all over. This idea was based on a paper where the writer of the paper said that the calcium/magnesium ratio for intake should NOT EXCEED 2:1 and for some reason this was taken by many to mean that it should BE 2:1. Calcium is important, though.
If you are really deficient in magnesium the level of magnesium stored in your bones has become very low and so your body is trying to conserve by not releasing very much from the bone. Because of this your body has to make more of the enzymes that use magnesium to compensate and when you have a sudden increase in the amount of the magnesium available those reactions make more of the products and you feel better. However, your body still wants to conserve magnesium so it lowers the amount of those enzymes and you feel worse again. The answer is to get more magnesium back into your bones. As long as your stores are low your body will be trying to conserve and you won't get permanent results from a change in your magnesium intake.
I am going to post about a way that we have discovered that helps us to get a lot more magnesium into our bodies using oral magnesium, so look for my post to learn more.
I learned about this because we have been having problems with magnesium deficiency and I searched for months to figure out how to resolve it. It sounds to me like you do have a deficiency from your list of symptoms and because you responded to magnesium and then it seemed to stop working.