please go to the doctor...i had a bloody nipple at 37, they did a few tests, found nothing and sent me on my merry way....but failed to tell me that i needed an annual mamogram and ultrasound...at 39, i was diagnosed with breast cancer and just had a mastectomy.
an inverted nipple is NOT a good sign. I dont want to scare you, but if it gets you to a doctor quicker and gives you a better result than me, so be it...Early dectection is key!
I had a simular situation, I was bleeding from my right breast. I suggest you seek medical care as soon as possible. Good Luck!