implantation bleeding?

Robbie
So my period was supposed to start on the 18th-22nd. Well at 11pm on the 16th I spotted light pink blood, then on the 17th my period started and it was regular since I never had a heavy period. Well yesterday night on the 18th around 10 pm I stopped bleeding. So my period was only two days long. So this normal or could this be a sign of implantation bleeding?