How to tell if you’ve had a miscarriage if you didn’t know you were pregnant?

[MGH254]

As the title suggests, here’s the backstory.
I had been off the pill for a few months (wasn’t getting on well with it emotionally). My partner and I sometimes used condoms but mostly were just “careful” (not the best option, I know...). I started the pill again to delay my period for a holiday, and stopped taking it on Tuesday, thus expecting my period to start today, which it did.

Started normally, I thought the cramps were a little worse than normal but not horrendous. Then when I went to the toilet (TMI warning) I noticed what I thought was a large clot on my pad. On closer inspection (as large clots are not normal for me) I noticed some white-ish tissue/fluid within and what looked like a sac.
Could this be an early miscarriage? I would be 6 weeks at the most. Is there any way of knowing for sure if I was pregnant? Just for peace of mind either way.

[Softscoop35]

You could take a pregnancy test? You could have HCG still in your system.

However, if its negative, it still wouldnt rule out a pregnancy/miscarriage.