Am I Pregnant?😔

Around ovulation my SO and I fooled around and had anal. He ejaculated in my bottom and then he leaked out. What are the chances of the sperm that leaked out to find its way to my vagina and get me pregnant? My period was supposed to come yesterday and it never fully did. Yesterday and today I have had on and off light bleeding. It's red. And I feel like my period might be coming but it's not enough blood for me to feel completely out of the woods. Could this even get me pregnant? Would implantation bleeding be this long and around this time anyway??