Low HCG - but doubling?

I’m currently 3w+6d. Spinning out over the past few days, any thoughts would be so appreciated (good or bad!) 🥹

See timeline below

- 8DPO - faint line on FRER, looking back it may have been an indent

- 9DPO - blood test was 3 hcg, so doctor said not pregnant

- 10DPO - fainter line then 8DPO, shadow was there but thought I was out this month

- 11DPO - stronger positive with pink colour, this threw me

- 12DPO - stronger positive

- 13DPO - blood test was 13 hcg, it’s technically doubled every 48 hours since my last test at 9DPO but nurse said it’s on the lower side

Anyone else have low HCG and have a positive story?