copying cells with a macro

I would like to copy a range of cells with a marcro, for example copying range C3:C15 over to D3:D15 and when I run the macro again I want range D3:D15 to copy to E3:E15 and from there to copy E3:E15 to F3:F15. I want to keep that going to the next and the next with the same macro. But it just keeps copying the the original range which I recorded in the macro, but I want it to keep going. If somebody can help me with that, I would sure appreciate hearing from you.
Thanks