I have a Rabbit and while it might be able to temporarily desensitize you if you use it a lot, I don't think it's capable of causing nerve damage. The rabbit ears are soft and flexible. I find it hard to believe that's the cause of your problem.
Could it be that your orgasms now are about the same as they were before you started using a vibrator, but the vibrator orgasms are so much more intense for you that the "normal" ones seem less strong now by comparison?
If it's any consolation, most women find it just about impossible to have a clitoral
orgasm in missionary anyway. It's simply not a good position for female pleasure.