Huge teen pregnancy scare. PLEASE COMMENT.

I was 3 days late on my period when I started bleeding. But this "bleeding" seems very VERY weird. It has only lasted 3-4 days when i usally bleed 5-6. But anyways. It goes like this.

Period day one: I awoke to a gush in my panties and found bright red blood. So i put a pad on. That day, the bleeding was a medium/light flow and contained no clots. The blood was dark/bright red.

Well, that night i changed pads ( of course ) and went to bed.

I woke up to this

Front of pad

Back of pad

And this is what it looked like when i wiped. There was a clot and some other tiny TINY clots

And after passing that clot ( as showen above) along with those tiny tiny clots, I only passed one more clot that day.

But right after i changed this pad, the bleeding tapered down to a medium/light flow.

Period day 2: as i said, right after changing that blood soaked pad, the bleeding tapered down to a medium/light flow. The blood was dark/bright red and that evening i passed one clot. ( as i said above. This one clot is the clot i passed after having passed that clot that had little tiny clots along with it that morning )

This is how it looked when I wiped that evening

Period day 3: The bleeding was a medium/light flow ( dark/bright red blood), but tapered down into dark red/brown spotting during the evening and became very light brownish red spotting that night. The bleeding had no clots.

Period day 4 (today) : I am only having brown, rust colored spotting. No clots at all and the blood is only there when i wipe. Nothing is coming out on my pad.

I am terrified that I am pregnant! I do NOT want to be pregnant.. ive learned my lesson from this scare. Im terrified right now.

Also, i forgot to mention: The blood seems to be more on the watery/thin side. And not thick like it normally is.

Somthing that seemed odd was my breasts hurt 2-3 days before the bleeding began when they usally hurt 1-2 weeks before i start bleeding. So that was odd.

I also felt kinda sick during and around my predicted ovulation date, along with weird muscle spasams in and around my uturus. I also felt these weird tingles in and around my uturus during and around my predicted ovulation.

Im terrified that this bleeding is pregnancy bleeding or implantation bleeding and not a period. Im so stressed.

Is this 100% my period? Am i 100% NOT pregnant? Or could this be pregnancy bleeding or implantation bleeding?