Bleeding (w/ flesh) during sex?

I (24F) had sex last night with a guy (23M) for the first time. It was in the dark and I wasn’t in any pain, he just kept telling me that it was really wet, I didn’t think anything of it. When we finished and turned the lights on, him and I were both covered in blood, and so was his couch (like A LOT of blood). I got into the shower right away and while washing off the blood, I noticed pieces of what looked like flesh in the blood.

I frequently get tested for STDs and had been tested since my last partner.

It wasn’t my period, I finished that two weeks ago and I can tell the difference. This blood was bright red. And after the shower, no more blood came out at all. I didn’t get dizzy or lightheaded at all.

This guy wasn’t very big nor did we try any positions I’m not used to. I have had frequent sex with 3 other guys (one of which being painfully large in length and girth) within the last 6 months and haven’t experienced something like this.

I have bled during sex before. But, this has only happened a few times over a year ago while trying a new position that hurts me a bit more, and there was only a little bit of blood in result of that.

I (drunkenly) had sex with a different guy a week ago (no blood) and he finished inside of me. I took a Plan B and saw the doctor after that to get tested for STDs and pregnancy. I know it was too early to check for pregnancy.

Is there a possibility that I had an early miscarriage? Result of taking the Plan B? (I am also on birth control and drink alcohol frequently.)

I have searched up this issue and none of the other causes I’ve seen fit into my situation.

(Just want to add: This guy was very sweet and caring about the situation. He saw me freaking out and had me get into the shower. We got all of the blood out of his couch. He wasn’t disgusted or mad, only worried and offered to take me to the hospital.)

(Also would like to add: I know many people will tell me that I should’ve gone to the hospital right away. But, I have a fear of the hospital/ER, and have felt completely fine during and since the incident.)