Five days ago i started having a miscarriage with heavy bleeding,large clots,& pain in my lower back & stomach.how long will this pain and clots last?

Until tissue passage: It will continue until you pass greyish/blue dark tissue mixed with blood which will be the fetal material. When that occurs, you need to contact your GYM MD.

Varies: If you are still bleeding 5 days later you need to see a provider to assess whether the miscarriage is complete or not.

Empty uterus: Once the uterus has emptied from all contents of an early pregnancy, the cramping will cease. On the flipside, if the cramping does not cease, likelihood is high that there are still contents, possibly as much as a blood clot, left in the uterus.