Dear cindyg, This lump could be a number of things, but having it biopsied would be the next step to evaluate that it is not cancerous. Having the lump removed would be an option if it is causing discomfort, or if there was question that an adequate sample was not obtained by biopsy. If the results of the biopsy are benign, and it is not causing any problems you could leave it be.
After this core biopsy, there would be some healing time involved but this should not interfere with breast feeding. You should of course check with your physician to make sure there is nothing in your individual case that would change that.