I offered an online (photo) consultation to a woman who was concerned about her nipple piercing:

Hey,
I've attached a picture of my nipple piercing. I've had it for about 3 months.

A bump has appeared and sometimes puss/blood leaks out of it. I think this is because I became less strict with salt soaking it daily, because I assumed it healed already. Do you have any ideas for getting rid of this bump and do you know if this is just simply and infection or is it worse e.g. Migration/Rejection.

My reply:

Nipple piercings can take 6-9 months or so to heal on women, so you will need to keep up with aftercare for some time. The excerpt below is from my book:

Tenderness may come and go due to the fit of clothing, sleep habits, physical activities, and other factors. Women often find that nipple piercings experience a flare-up (secrete, swell, or become painful) just prior to and during menstruation, even well after the healing period.

Nipple piercings can take a long time to heal completely. They may regress for no apparent reason after many months of stability. Should your piercing take an excessively long time to settle, try different jewelry or change care regimens until you figure out what works best. This experimentation can require patience, but adjust at least one aspect before giving up. If you endured the procedure and some of the healing period, it is worth preserving the piercing.

You will probably find that the support of an undershirt for men or smooth-cup bra or sports bra for women is helpful for your comfort and protection, including while you sleep. A minute or two after settling into a tight garment, the piercing usually feels less tender. Men who are not partial to sleeping in a shirt can wrap a length of clean Ace bandage across the chest and around the body. This type of elastic bandage protects the area while still allowing it to breathe, and it avoids adhesives that could irritate skin or pull hair upon removal. A disposable nursing pad or cut-to-fit piece of panty liner worn inside a bra will absorb any blood or sweat and will also help to conceal your jewelry.

From what I can see, there's no evidence of migration or rejection. It looks like you may have what I refer to as a "localized piercing pimple."

In my book there's information about how to identify it and suggestions to try. 

[If you sign up for a piercing problem consultation, I can evaluate your specific situation and provide advice. Note that there are other types of bumps piercings can suffer from including excess scar tissue formation and overgrowth of granulation tissue, and each requires different interventions.]

These are the care instructions I suggest, and saline soaks may help to facilitate healing and minimize secretion, but you must do them correctly (if you are having any bleeding, you should refrain from the soaks).

Also, do you know what material your jewelry is, and if it is internally threaded with a mirror finish (see photos)? If you are not wearing high quality jewelry, you may need to change to higher quality jewelry for your piercing to heal properly.