Does Blister At The Site Of Mole Removal Need Medical Attention?

My son had a mole removed by a doctor. It was not cancer. He only required one stitch to be taken out two weeks later. Everything seemed fine and the stitch was removed. Then I noticed about a week or so later that it looked like a pimple was forming. It has now been a little over a month and the pimple or raised skin is still there. Should I be concerned? Should I take him back to the doctor? or is this a normal process for healing?