I have only one side of a rigged model. I need to make it whole, not only a half. I try to duplicate and mirror it, then I do the same with the armature. But, the duplicated side of the armature doesn’t do anything, and the original side of the armature controls both sides 
anybody got any suggestions?
Check your weight mapping… sometimes the weights get lost or screwed up when mirroring. Also, you’ll have to apply the mirror modifier before the armature functions correctly on the mirrored side.
I usually wait to rig a character after all the modeling is done, that way, if you have to delete one side in order to tweak something, Blender will do a really good job of flipping over the correct weight mapping once you apply the mirror, assuming all the proper vertex groups are present first.