4 weeks - low HCG

I’m looking for stories good and bad of low HCG and the outcome. I’m receiving fertility treatments and my doctor said I ovulated 17 days ago. I was supposed to test Monday at 15DPO and it was negative. I tested this morning since I hadn’t gotten my period and I got a VERY faint line. I called the clinic and got a beta blood test. My HCG was only 9. It’s possible I may have ovulated later than they think I did and it’s also possible I implanted late which means I might have only JUST started producing hormone OR this is a chemical. Any stories of low HCG at the start positive or negative? Much appreciated