Yup...ovulation predictor kits are the way to go. I also have a 28-day cycle but I ovulate on day 11-12 - a little earlier than "normal". The best way to know for sure is to buy a kit.
I agree with Pum. I would also try ovulation predictor kits. They can help you pinpoint your most fertile days. Good luck!!
Assuming you ovulate around day 14 (a good assumption as you have a 28 day cycle) you should try to get pregnant around then ie starting on day 11 and going through to day 16. Go for it as often as you can manage, every second day as a minimum I reckon.
Good luck.