Implantation?

Amber

How does implantation work? For my first two I never had any bleeding. I was late for my period for 4 days. Then it finally came the first day it was medium flow and dark red blood. I usually have heavy periods. The second day it was much lighter and pink in color and spotty. Now today I have no bleeding or spotting at all just crampy and extremely tired. Is this a period that only lasted 1.5 to 2 days or is it implantation?