Miscarriage?

Patient: Had a brown discharge for a week, then got my ‘period’ on thursday then on friday had constant severe lower abdomen pain and backache, on saturday evening a passed a blood clot.. ( which i never ever ever have got before, and i never ever experience and period pain what so ever! Done a pregnancy test on friday it was negative.. Could i have had a miscarriage? and is my pregnancy test negative as my HCG levels could be too low to detect?

Doctor: