Ovulation

Is it possible to ovulate really late one month and then early the next? Last month af arrived on day 35 which only happened that late one other time in the past year. My cycle was usually around 27-29 days. I ovualted around CD 25. I first thought they were af cramps but then it never came. Now, I'm on CD 12 and I had some pain in my ovaries that felt like ovulation. My cycle was a little off in May because I was on Clomid for only 1 month, but I had regular cycles after that for 2 months. For the year that I've been documenting my cycles, af always comes on 12 or 13 DPO. I actually though I might have been pregnant which is slim to none given our situation. My dh has low sperm count, motility and morphology. We're heading into ivf this month. Thanks, Lara