When should I expect to have cramps/heavy bleeding

I’m pretty confident I’m having a miscarriage (long story short-I’ve been spotting and went in for dating ultrasound and I am 2 weeks behind, I know when I ovulated based on tracking bbt-showed 6w1d and I should be 8w1d and they couldn’t get heart beat bcuz they said it’s early). I’ve been spotting (light) the past three days. No cramps or heavy bleeding yet. When should I expect this to happen?