Ovulated late

So my partner and I have been TTC for a while now. I was using the ovulation tests and every month I would always ovulation on day 15 without fail. I stopped testing this month to give myself a break but started getting cramps a few days after day 15 so I tested and seems I ovulated three days later than usual. What does this mean? Why would this happen when I’ve been so regular all the time prior to this? Obviously now I know I won’t get pregnant this month because we missed it. I have started working out more at the gym, can this affect it?

Sorry after TTC for so long I guess I’m a little nervous about it. Thank you in advance for any suggestions