Regardless of what HPT's claim (Test positive as early as 6 days before AF) actual statistics show that the most sensitive test will only show positive for 20% of women 2 days before missed AF and for 40% of women 1 day before AF. Showing positive at 7 dpo is not even remote, it's impossible. Implantation doesn't even occur till, at the earliest 6 dpo and even with that it still takes 3 additional days for the implanted egg to send the signal to release the HCG hormone to the body. Hence the women who test positive at 9 dpo. But testing positive at 9 dpo is really rare as most women implant around 10 dpo and test positive by 14 dpo.
Don't lose faith, Ive never had early symptoms and have always found out by a missed period. As hard as it is ... I would wait a while to test again ... At least 10-11 dpo.
Good Luck on your BFP.