I fill some thing hard in my right breast and it is tender to percussion but I felt it this night and I am breastfeed a baby of 12 month?

Possible clogged duc. Possible clogged ducts or mastitis, the way you describe it. Warm compress and continue breast feeding. If yo uhave fever or if the pain ets worse or if there is redness around, you might need to get to the physician for antibiotics.