I was also very regular before taking Clomid (every 26-28 days) & after taking it, it did make my periods more difficult to predict. Sometimes it would be shorter than 26 days & sometimes it would be longer than 28 days. I did go back to normal when I stopped taking all the infertility meds & doing all the infertility treatments. And after I had my twins (who are 4 now), it also went back to normal even when I was still breastfeeding (unfortunately for me!).
Good luck to you as I know it can be a long & difficult road when you are trying to conceive.