Dear librarylady: Typically, breast cancer is not painful. Having said this, if you have found a lump, you should see your doctor. If he/she feels this lump, then a determination can be made as to what further evaluation may need to be done.
any new lump in the breast needs to be checked. See your doctor. If it's tender it's less likely to be serious; but you MUST have it checked!!!! No online guess is possible, or meaningful.