Why would one piercing get infected, but not the other? And how do I help...

[Pierced'n'Tattooed]

...it heal without meds? Almost a year ago, I got both of my nipples pierced. I followed my aftercare instructions to the letter, and they were healing beautifully, until about a month ago. Out of the blue, my right nipple became swollen, painful, and started oozing. My left one, on the other hand, is perfectly fine. I tried to stop the infection by keeping it clean and doing sea salt soaks, but that didn't work, so I ended up taking amoxicillin. It cleared it up quickly and I was fine. This week, the right one (but not the left) started getting infected AGAIN. I just don't understand why my piercing would start getting infected out of the blue like that. Also, why would one and not the other? They both get the same care. I clean and rotate them every night in the shower. Any thoughts on this one? Also, is there some way I can stop this from getting really bad again without meds? I'm uninsured, so I really can't afford it. The last thing I want to do is to have to get rid of my piercings because they keep getting infected (and I know not to remove them, especially when they're infected). Any advice?