It is possible, yes, some women just don't have as much cm as others may. Have you talked to your doctor yet, as generally they want you to go in for some info/test/advice once you've been trying for one year? Also, trying charting your basal body temperature. ("bbt". go to
Ovulation Calendar and Ovulation Chart - FertilityFriend.com for a handy chart and helpful hints.) this will help you get a better feel for your ovulation timing.(in conjecture with your opks.)