Unfortunately, you really don't give us all the info but I will answer based on what you are telling us. First of all you should discuss this with your surgeon. If you truly had a mastectomy, whether or not nipple sparing, I doubt you will regain sensation as the nerves that supply erotic sensation are removed as part of the mastectomy. Again, spend some time talking to your doctor as he or she will know better than we will. Good luck
There are some missing details here regarding exactly what kind of surgery you had and what the condition was that was being treated. But presuming that it was a nipple sparing mastectomy, unfortunately there is very little likelihood that you will ever have much feeling in the nipple again. Time will tell over 2-3 years but if you needed a mastectomy, sensation needed to be sacrificed for your health. Good luck.