so this is my 2nd month trying the OPK. first month was invalid the entire month, and I only had 8 tests. Now I bought one that is cheaper and comes with a bunch so I've been testing every day so I don't miss my window, but the month is almost over for me and the lines have never been darker or iqual as the test line..... I still had sex those days and considered them fertile days....... this has happen twice this month... is it possible to ovulate twice a month?