7 weeks pregnant please help?

I am currently 7 weeks pregnant. high risk. i have seen my baby on the ultrasound quit a few times. and there is always a heart rate and its a strong heart beat that keeps getting stronger each time and the baby is growing. the G Sac is measuring 4 days behind but they said thats fine well my problem is that i have been having my hcg checked and they have been doubling every 2-3 days untill this last time it was 25000 and then the following tuesday it only went up to 37000 so it didnt even double in 3-4 days. But the same day that last one was taken they did an ultra sound and the baby had grew and the heart rate is cont. to rise. they said the baby looked great. so shoudl i worry with this hcg levels? i have also had really bad cramps this entire pregnancy...its my second(well 4th but had two misscarriages) if you have had a similar problem please let me know the outcome of it. i am so scared that im going to loose this baby. please help