What Causes Irregular Periods While Trying To Conceive?

Hi Dr, hope you can help me with this I'm 32 years old, married just over a year and have been ttc since the summer, I would have had a regular period between 28/30 day cycle, but since we have been ttc it has changed to a 40day cycle, ovulating on the 23day, bought the clear blue ov tests, this mth I had a 30 day cycle & ovulated 2 days before I got my period, what do you think would have caused this, really want to become a mum!!