Don't know what to think?

I had a missed miscarriage a month ago. Had to take the pill to bring on the miscarriage. I passed tissue on 19th Feb. I ovulated around a week later and we tried. Now I've been back to hospital because I'm still getting positive pregnancy tests, the same day I got a positive ovulation test.

I've been back to hospital and they are satisfied that I've passed all pregnancy tissue but I still got a positive pregnancy test the day I had the scan.

I'm back in 10 days to hospital for another scan and pregnancy test but how can they tell if it's old or new pregnancy? They don't do blood tests for pregnancy in my country. Maybe I could ask but is there any other way of knowing it's new or old. Will be too soon to see anything on a scan.

Period would be due in 4 days. I took below test this evening.