Some of the side effects of excesive magnesium intake are dehydration and dry skin - this normally happens due to a poor diet and/or lack of calcium in the diet. Do a google and look for foods rich in calcium or consider some supplementation to balance the extra magnesium. Alternatively, cut back on the mag oil ... your body is telling you you're using way too much.
The salty taste in your mouth is likely to do with a chemical change in your saliva due to dehydration (note how tears are salty) so I suggest upping your water intake and cutting out on any sweet drinks or caffeinated beverages if you drink those.