Is misscarriage painful ? And how long after miscarriage will the pregmancy test be negative And how do i know is miscarriage

I had 2 miscarriages at 18weeks & 8 weeks. 18 weeks was painful with contractions and bleeding for about 3hrs. I had to deliver the baby out (stillborn). The next day, doctor made arrangements for me to go for scan & cleaning to make sure my womb is clear. My 2nd miscarriage was just heavy bleeding. No pain. Again doctor will do a scan to make sure womb is clear. No test was done on me.