opk...help!

lauren • TTC #1 for 2 years, unexplained infertility, 3 failed IUIs, now doing IVF w/PGS
I've been testing all week, but I'm not sure if the 26th is actually positive. It's darker than the rest but not darker than the test line I don't think. I tested again this morning (27th) with a cheap online test strip and it says negative. Any advice would help!!