To me they look fine for two days after a missed AF. Do you know when you ovulated? Maybe you ovulated a little later? Or maybe your baseline hCG level was very low (like 1) and you implanted late?
Implantation happens anywhere between 6-12 days. So if you implanted in the middle at around 9 dpo (5 days before period) and your base level hCG was 1, you would only have a hCG level of around 16mIU/ml eight days later (if doubling happened every 48 hours). And a level of 16mIU/ml would be quite faint on a test. You can't compare pregnancies either as every time you might ovulate or implant differently, or your base level hCG might be higher or lower. For example, if you implanted on 8dpo with a base level hCG of 4, then your level eight days later would be 64mIU/ml, which would make a really clear positive line on a test.
I know it's hard (I worry too!), but not to worry too much!
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