Hcg levels?

I had an early miscarriage last month, hcg went down to zero. Without having a period I tested positive on 3 HPT this month. I have no idea when I ovulated after the miscarriage but the chemical pregnancy bleeding started on 6/22. 7/20 tested positive again. On 7/21 hcg was a 24. 7/23 41. Retesting tomorrow. Anyone else experience low but rising hcg? Especially after an early miscarriage?