I don't know what time of day you are doing the tests but it is said not to do them before 10:00 and after 2:00 is ideal. There are several sights on-line to get cheap strip tests if you are interested. I am the type to test 3 & 4 x a day :0) Although I thought the on-line test strips weren't working for me I actually got my first + at 8:30 am. I would only recommend testing this early if you are a freak tester like me with a handful to spare!
Also look into the natural ways to try and determine if you are ovulating like taking your waking temp (search basal body temp to determine ovulation). To increase accuracy you can combine this with observations of cervical mucus and can do cervical position too if you so desire. Sounds like a lot of work I know, but once you get the hang of it, it is second nature. If you'd like more info you can search for info online and message me with any questions you have. If you are interested. Also this kind of charting can give doctors TONS of info about what might be causing the problem if you are having trouble conceiving. Good luck!!
I too only had negative OPK tests. I even did 3 test kits in a row, and still nothing. Some people say to test twice a day, because your surge could be very short and may only have a 12 hour window, which only adds to the anxiety. I would have liked to try it, but it was hard to stomach the $30 for each kit.
You could still conceive naturally. OPK's are not effective on everyone. Most of the time, it is because you ovulate at times you least expect due to stress, anxiety, or life events as well as most women don't ovulate every month too. Best thing to do is to determine when your most likely fertile window is and just bed as often as possible during that time. If after 6 months to a year of no success, then you should seek medical advice from your doctor, to determine if there is another cause that needs attention. Most doctors won't help a couple until after one full year of trying first, if you are under 35.
Best of luck