Pregnancy question of conceiving

I started my period on May 10th, and had unprotected sex on May 11th. I do take birth control ,but lately i have been taking my birth control at 3-4 hrs off a few times (I forget). The birth control is a combination pill. Today May 27th. I was in the shower and touched my vagina and saw that there was light pink blood on my hand. Not sure if that is implantation or it’s just spotting from my birth control. I also don’t know how I would calculate the day of conceiving and much more.