Help please... how do you know if you have had a miscarriage if you dont even know you're pregnant !?!?!?

A while back I took 2 pregnancy tests a week after sleeping with my boyfriend, obviously it must have been too early as they came back negative. a couple of months later i was out and unfortunately i got hit in my stomach, the night it happened i began to bleed but not too heavy i had to be careful when standing up as i felt sick as soon as i stood upright. i bled for a week which i noticed was leaving my body in clots and also black, i also had severe lower abdominal pains which caught me off-guard and on numerous occasions i nearly did collapse I ended up going into hospital where the bleeding calmed down as i was lying down most of the time, but the stomach pains weren't budging, i told the hospital i hadn't been ually active in about a year so i don't think any further pregnancy tests were done. I had an ultrasound but my bladder wasn't full at the time and i was told there and then not much would show up because of my age. i had an x-ray of my stomach again nothing showed up. I was let home the pains still continued and i have been bleeding for about 7-9 weeks since all of this and i really don't know whats causing this. please can somebody help i am really confused as for some reason i just feel different, i feel like somethings missing, my moods are all over the place and i am very snappy one minute im happy the next im as low as u can be and i don't know why ... i just want to know the truth.