I never got a dark line on the OPKs?!?!?

The hubby and I are TTC and I normally do not use OPK but I did this month and am confused as all get out! My LMP was 5/23/11 and my cycles vary quite a bit from 28days to 37 days with average being 33. I started using the tests right after my period ended and continue to use them daily. I was with my husband on vacation on June 6th-14th. I figured I should have ovulated around the 9th or so. I took atleast one test a day but all at random times and all had either have no line or a faint one. Perhaps I was not waiting long enough for the line to get dark? Or did I really not ovulate? OR is it more likely that I ovulated but it didn't pick it up? Tomorrow is day 28 and I would be expecting my period sometime this week and I am really really hoping there is still a chance (a good one anyway) of having a positive pregnancy test. Thanks!