Help!!

I had a positive test yesterday on pregnosis brand and it was a clear positive in the time frame. Used the same urine with FRER and got the most faint line. Today I only had a FRER to test with and the line is the same? I thought FRER is suppose to be most sensitive? It’s bearly visable on FRER. On pregnosis at 8dpo I got a faint line, next day it was a lot stronger so I know my HCG is going up.. just wondering why it wouldn’t be showing up on FRER as strong as the other test.. don’t think it’s a chemical pregnancy, no cramping and no bleeding..