I took vit c earlier 500mg and I have quite a bad headache. Is this normal? I also get 80% RDA from another vitamin supplement. It says on the vit c "do not exceed stated dose" - does that mean I shouldn't have taken my regular vit?

I'm also taking glucosamine for the muscle pain I get (some days so bad I can't do much at all except go for a walk, watch tv, computer for a bit and lie down). Also I am now taking magnesium.

Is it ok to take these stuff or an I stirring up mercury? For whilte I was taking iron to see if it helped the cycles, but it didn't so I stopped.