OPK help needed!

Louise
Hi ladies please help :)
​I have been using OPKs and yesterday 10:15am I got a visible test line  still lighter than the control, today I tested at 12:15am and the test line was even darker - almost positive but not quite.
​I just tested again this evening 8:30ish and no test line at all :( 
​Did I miss my surge or did something happen?