Haih, at 8 DPO the hCG injection (Hucog) should mostly be cleared out by now lah, usually it takes about 7-10 days depending on the dose they gave you. Since you're not seeing a second line yet, it could be the injection is still lingering or it's just too early for implantation hCG to show up, so best to test again in a few days and see if you get a proper progression! I know the waiting game is so stressful, a few of my mum friends who did fertility treatment say the anxiety during this window is real, but do be patient with yourself because the numbers should climb properly if it's a true positive. If you're unsure, maybe check with your doctor, they can order a blood test which gives you the actual hCG numbers and takes out the guesswork from these home tests.