call your doctor and ask if this is normal. Somethings to look for is redness, burning, hot feeling, oozing, sore to the touch or fever all these things indicate an infection.
It's probably just scar tissue. Where I had my incision for surgery, I have a couple of little "knots" If your lump bothers you, You should call let your doctor know, a nurse or assistant could let you know if you should be concerned.