I think I'm about to miscarry

I took 3 pregnancy test in June they all came out positive, had a pregnancy confirmation that was also positive. I've hard cramps here and there nothing serious, except I've had sharp pains throughout my whole stomach for a few days besides that Every thing has been going fine until yesterday...I noticed I had dark brown discharge of course I panicked so I went to the ER they did an ultrasound and said there was no heart beat but because the blood they took is actually showing I'm only 4 weeks instead of 7 weeks. The nurse did say my levels were very low. Today I've been bleeding passing blood clots as well, I'm more then sure I'll probably have a miscarriage.