You should always be concerned about lumps in your breast. You need to inform your doctor and get them checked out. Most likely they are related to breast feeding but you need to make sure.
If the lump in your breast hasn't changed in size or has grown you should be concerned and evaluate the mass that remained unchanged to rule out malignity possibility.
They might be due to blockage of residual milk or due to hyperactive milk-secreting glands. For tender lumps, massaging will do the needful. It is advisable to consult your doctor.
