Did I miss it??

I started testing at CD11 and as you can imagine the line was pretty pale, it gradually got darker and on CD 14 was the darkest test I had but still not positive. So today CD 15 the test was equally as dark but not darker or lighter. If I was due to ovulate today, I would have expected the test to be a bit darker, so I guess my question is, could my surge have happened overnight and now I'm coming back down? A bit more info, I take my test at the same time everyday (around 2.00pm) after holding urine for at least 3 hours and not drinking too much so as too not dilute my urine.

The only thing is my tests do go out of date in September, could that affect it? 

Thanks in advance for any advice anyone can offer!