Need a lot of hope

I took an hpt last Wednesday, and it was positive! I was over-the-moon excited. Thursday, I had blood work done, and my hcg (20.7 mIU/mL) and progesterone (3.54 ng/mL) levels were low. I went back on Monday to have more bloodwork done, and my levels went up, but didn't double. My hcg is now 21.8 mIU/mL, and my progesterone is 6.98 ng/mL. The nurse seems to think its a chemical pregnancy, but my doctor has been out this whole time and hasn't looked at the numbers. Has anybody else had levels this low?