Positive Then Negative.. Which Is Right?

Renn

I took the test when I was 15DPO and I thought it was negative cause I didn’t see the faint line.

Bought three more tests and used 2 today being 16DPO and came out negative. I also drank a lot of water before this but don’t know if that matters.

Should I take an OPK and another test tonight with minimal water consumption?

Thanks for any help!