TMI: HGC after miscarriage!?!?

Hello ladies first of all I am so sorry for your loss(es). I hope this is just a silly question and I'm grasping at straws, but help would be very much appreciated... I miscarried at (12 weeks) on 8/16 my levels were in the 3,000s they took blood again on 8/18 and they were in the 2,000s. I naturally miscarried on 8/19 and was still in pain I literally reached up 8/22 and could feel some hanging out!!! The best day, 8/23 it hadn't moved so I made an appointment with an OB and he removed the sack!(No idea on the the fetal development). On 8/30 he had me come in for a urine test (positive) so more blood work..the levels were at 24... He cleared us to have sex with a condom so we just used the pull out method on 9/3 I had a gut feeling (silly I know) and let him cum inside... 9/5 we went back in for more blood work and my levels were at 10!?!? Why such the slow decrease??? Now he wants us to came back in 9/13 for another urine test? I thought that only read 20 or above? Is he assuming I'm pregnant again already or is that silly!? Why are we doing a urine test instead of blood work? I've been looking for answers online all day but can't seem to find an answer! Please help I'm so confused!!!