Am i pregnant?

So, I have irregular periods, so I'm used to it being late, but I also have a heavy flow as well. I started spotting last night and it was bright pink, and now it's a little stream of bright red blood, but it goes away and comes back randomly. I'm having back pains, cramps, and sharp pains in my front abdomen and my breasts have started hurting a bit since I've started bleeding... I've taken two tests, and have gotten a bfn.. is it implantation bleeding..?