Do I have to wait for HCG to drop to 0?

Tiffany • Beautiful DD Caroline
Does your HCG have to be 0 before you ovulate again. 
My story: 
They suspected a miscarriage last week. It was confirmed today. Basically my first appt 5/23 HCG 15 progesterone 2.52 2 days later started bleeding the next day 5/26 HCG had went up to 34. Not great but still doubled. Next text was 5/30 it had only went up to 54. Bad news (that's like a doubling time of 100 and some hours) told me to expect some bleeding and to come back in a week (today) to retest. HCG was down to 18 today. Still considered positive. But definitely miscarrying. 
Long story short I haven't started bleeding yet (at least not since 5/25. That was for a couple days but they told me that prbly wasn't the MC since my levels went up after) so when can I expect that to happen? Also when can I start trying to conceive again. Does HCG have to be 0?