Implantation

Can someone explain to me how implantation bleeding looks and works? How is it not suppose to be able to fill a regular tampon or pad if it can last for 2-3 days? My period is due in 5 days. I’ve had horrible migraines and tender breast/nipples and I started bleeding this morning. I wiped and two drops were on there so I stuck a tampon in and pulled it out just a little bit ago and it was half way full of red blood no brown like the normal start of my period. Could I still be pregnant?