Bfp or bfn

So I took two test at 9dpo and got positive and took about a total of 5 more this week and with a cheaper brand the line got light and lighter until I got a bfn today. I'm want to know has anyone else had this happen with the cheaper the brand the lighter the line got. Af is due Saturday 9-26 so I have 4 more cheap test to keep trying with but want some insight