Miscarriage almost 13 weeks ago

I had a miscarriage almost 13 weeks ago when I was 6 weeks 6 days, I’d be 18 weeks 5 days now, I bled for about 10 weeks on and off, I think I just started my first period since my miscarriage and this has just come out of me when I went to wipe, does anyone know what it could be? I have had unprotected sex with my boyfriend since but I doubt it could be new