HCG didn’t double

Paulette • 28 weeks Pregnant at 38 y/o after 5 miscarriages

Hi wondering if anyone had any similar experience and how did it turn out. Because of previous miscarriages my doctor sends me for HCG every 2 days. It went from 230 to 593 to 2200 to 6600 to 12,800 so doubled each time. But the results I got now are only. 17,500 which didn’t double… they went up but not by a whole lot…. It still only 5 weeks and 3 days shouldn’t it still be doubling?