Can I be pregnant?

Hi everyone, I'm new here so I'm just getting a feel for how things work.

I have a few questions and I'm curious about your experiences with this.

I know I should probably see a doctor, but I find it nicer to ask here first.

I've had a 33-day cycle for 5 months now. I'm not using any contraception or other birth control.

My last period was on August 15th. About 1.5 weeks later, I got some bleeding. It wasn't as much as my normal period and was actually way too early. It only lasted 4 days, whereas my periods usually last around 7 days.

Could this be implantation bleeding?

After my August 15th period, I wanted to start using ovulation tests (I only needed a few, so I had plenty left over).

Yesterday and today, I did an ovulation test 'on a whim'. Both were positive (I didn't use first morning urine or avoid drinking fluids).

My next period is due on September 17th.

I'm looking forward to hearing your experiences and tips.

Thanks everyone!

Best, Naantje