Why does one of my nipples only get hard and stick out?

Hi. I presume you mean areola (the pigmented part around the nipple) - 7 out of 8 women have minor differences between their breasts in terms of nipple position/volume/position of the crease under the breasts, so this is normal. If you look at some of the photos on the link below you will see...

Many women with inverted nipples find they have no problem breast feeding, while others do not even try, having been told that it is not possible with inverted nipples. Certainly the degree of ductal tethering (and the resultant severity of inversion) has something to do with being able to...

It is not uncommon to have an extra nipple on the chest (anywhere from the groin area up towards the armpit) - in both women and men!  They can be removed with a relatively easy procedure.   Seek out a qualified surgeon who does breast surgery for a consultation.  A good...