Mastitis?!

Has anyone gotten non-lactational mastitis? It’s a breast infection in woman who ARE NOT breastfeeding. It’s actually common in women that are breastfeeding due to the baby bitting, etc. But I managed to get it in my right breast and I’m 20 never been pregnant so never breastfed. I’m just confused and even my doctor seemed confused and I went though a round of antibiotics and am feeling a bit better but still doesn’t answer why I would get this in the first place? And I’ve also got an ultrasound the first time I went to the doctor and the radiology doctor told me he saw nothing concerning, yet when I go back for the follow up with my GYN, she said let’s repeat the ultrasound to “make sure what they saw is gone”. I also have cold and was a bit disoriented so I was dumb in not asking “what did they see?” But after my second ultrasound, the same doctor just quickly scrolls though the pictures the technician showed him and said the same thing “don’t see anything concerning”. I’m just still confused. Has this happened to anyone? Should I do other testing just incase. Cause of course google searches just tell you you might have cancer 🙄 help anyone? Thanks