I was about 6 weeks pregnant when I had a little spotting in the evening. The next morning, at work, I had a massive cramp and then a huge amount of blood. There was no question in my mind that it was a miscarriage.
I ran up to my fertility specialist and they took an ultrasound. The doctor told me "Well, someone is still in there." Sure enough, she showed me the dot that was my future son and the heartbeat. There were also signs that something else had been there - not a twin, but I think it might have been the failed remains of a start of a pregnancy from the previous month. That's just my thought - it was never confirmed. I'm not sure if that's what caused the bleeding.
She told me I was having a threatened miscarriage and I was sent home for the weekend on bedrest. After that, everything was fine.
Wishing you the best and hope that everything turns out fine for you too!