What Does A Decrease In HCG Levels Indicate?

I have PCOS, with my last round of 3 clomid with a trigger injection. Follicle scan showed possible ovulation. I have had zero bleeding, but cramping. I am now 18 dpo and I had an hcg blood test done 16 dpo and it was 35 but today s test was 33. My doctor suggested it was most likely the injection still, but I had done home pregnancy tests and there was negative tests during the 2 week period. I am still having pregnancy symptoms, but I am wondering if this is actually a miscarriage.