Yia sou Angele,
Most probably you have an FAA PPL/IR.
In addition to what SkyM said above, you will need to do at least 2 instrument approaches (one of them has to be with one engine inoperative) if you want to add the instrument rating on the multi-engine. If you choose not to do it, then the multi-engine rating will be limited to VFR flight only. So its worth to do the approaches anyway. If you have any questions PM.