When will HCG drop so that ovulation can happen


I had a D&C; 7 days ago. Prior to that I bled for 6 days. The baby died at 6 weeks. I took a test today and HCG isn’t gone yet but in order to avoid a lab copay I’m curious when the test will be negative? I’m thinking to re-test maybe in 3 days? Just wondering when I’ll be fertile again. Thoughts? The app says I’ll be ovulating in 8 days. I know that could definitely be off given that HCG isn’t gone yet... I’m just trying to pin point fertile window as me and SO don’t do the deed every day.