Bfp then bfn

Today I took a first response as I’ve been getting faint lines on internet cheapies. I left the test on the side and came back within 3 mins and the line was there plain as day but not dark as what my others have been at 13dpo. I had cramping at 9DPO which is my bfp is right could have been implantation?? I then got my other batch of frer through the post and decided to test again and this time was a bfn not even a hint of a line at all!:( has anyone had a faint line this late and it been a bfp or is it just my eyes??