Implantation bleeding

I need help I'm not sure what implantation bleeding is or how it works I'm confused lol about 4 days ago me and my so had sex and the next day I had pinkish discharge when I whiped so I thought I started my period well I didn't bleed or any thoughts rest of the day I'm taking metformin and I'm suppose to start clomid on the third Day of my cycle ?? What do I do!!