Could I be pregnant

So me and my boyfriend had sex last Saturday and he came inside me I immediately took a 
plan b  nothing I had no side effects just a slight head ach the week went by I took a pregnancy test either Tuesday or Wednesday it came out negative and Friday I was bleeding I thought it was implantation bleeding but then I also bleed Saturday and today which is Sunday I bleed for 3 days but now it stopped and I'm having like A little  bit of blood in my panty liner idk I'm scared I'm only 17 and I can't do this 😔
Should I be worried am I pregnant