Sorry to hear about your condition. Reconstruction after mastectomy
is associated with certain complications and it seems that you are suffering from those. The nipple reconstruction which was carried out must have necrosed due to less blood supply and the problem would have got aggrevated due to infection. Did you receive radiotherapy after surgery as well? Sometimes radiotherapy reduces the blood supply to the flaps and can lead to such complications.
You should consult your breast surgeon and plastic surgeon for these problems. If the flap is not functioning properly, you can discuss tattooing of the nipple..something which is associated with less complications.
Hope you get well soon.