I am going to do my very best to try to assist each question and concern. To answer your first question, yes, there are ovulation kits that can tell you when you are ovulating and the best time to try to conceive. The following link will tell you more about that, and how to obtina them, use them, etc,.
Go to: http://www.testsforless.com/?source=google
Next: Being overweight has proved statistically to hinder conception.Often, just loosing 10-15 lbs, can kick the ovulation cycle into high gear and promote conception.
As for being sterile? This can be verified by testing, although the cost would vary depending on the extent of testing involved, and who it is obtained through.
Another thing to mention: Certain studies have shown that the very stress upon us worrying about not conceiveing might actually be preventing the conception. So above all, relax and try not to think about how much you want to get pregnant.
I am going to include another link that might be useful for attempt to conceive by natural enhancers. Please click on the following link: http://www.womenfitness.net/conceiving_naturally.htm
And in addition, here is another source to assist in ways to possibly conceive: http://www.fertilitext.org/p1-101/
If you need anything further, please write again.
I hope this information might be helpful, and I wish you the very best.