Ovulation surge two days then btwn no surge????

I have the clear blue easy digital ovulation kit. I used it the first time and was able to get pregnant the first time. I have save the sticks from the last cycle to use now. Now I am having difficulty with this kit. I began testing early and I have received two smiley faces approximately three days apart and in-between those days I had just the circle. I wasn't able to test CD14 this morning because I went to the bathroom in the middle of the night so I tested later in the day and received a circle when the day before I received a smiley face. I am very confused and believe the monitor is defective. We are really trying hard this time because even though our first time we were successful at getting pregnant I miscarried. I received a surge on CD 10 and CD 13 as I said btwn that time there was no surge. Your assistances would greatly be appreciated.