I've had 2 miscarriages and a healthy pregnancy! Labor is so much different then a miscarriage...take the miscarriage pain and multiply that by 100 and you get what labor feels like! When you are in labor with a full term baby the contractions are very strong very intense and last longer...for an early miscarriage you experience cramping more then contractions. You say you passed blood clots the size of a 5 yrs olds fist...try to put into perspective a blood clot and a cantalope (babys head)
...blood clots are squishy and small compared to a hard solid cantalope...right there is another point that labor will be worse then a miscarriage! Good Luck!