HCG levels

I had a miscarriage 11/23/23 at 11 weeks. Have not needed a D&C at this point. Have been monitoring my HCG which started at 6000 that night. I was originally told that when my HCG was down to less than 5, I’d be clear for sex. Two weeks ago, it was 9. Last week, it was exactly 5. Yesterday, it was 3. Now, my OB is out and the covering OB wants me to come in for an ultrasound. Has anyone ever had retained tissue and tested so low (3)? I can’t find anything that indicates this could be a problem and I would like to TTC again. My kids were in the car so I wasn’t able to ask follow up questions yet.