In most cases, you should have had the FRN before taking the test. In our VEC we won't let anyone even take the examination unless they have already obtained an FRN through the FCC ULS. If they show up at the exam site without one, we will assist them in obtaining one on the spot.
If you didn't have an FRN when you took the examination, it could explain why it's taking so long for your call sign to show up. Again, I suggest you get in touch with the examining team and ask them to look into it.