Ovulation

My husband and I have been trying for our second for three months. I'm using ovulation sticks just to keep track of everything. The first two months I ovulated on the 13 day from the start of my period so this month I didn't start the ovulation tests until the day before I expected to receive the positive. However, I did not get a positive that day or any day following. Is it possible I missed it, or did I just not ovulate this month?