Clomid can and often does change your cycle. If you have a shorter cycle, it can often make it longer. Ovulation is not guaranteed at all, let alone on day 14!!

I remember when we used Clomid - I hated it because I had no idea when I was o'ing! We used the Billings method (mucus) to identify O, but since Clomid reduces and changes mucus, I felt totally in the dark - totally hopeless when it came to trying to work out when O was happening.

The best thing to do is get lots of monitoring done (which our old FS didn't want to do for us). Get blood tests and an ultrasound or two done so you know exactly when you are going to O, so you don't miss it.

I think a higher dose of Clomid may make your cycle longer than a lower dose - since it may take longer for your body to recover the estrogen. It probably depends to, on whether you normally have a lot of estrogen, or have been estrogen deficient (which I had been just before starting Clomid - so Clomid was horrible because it made my estrogen levels go sooo low - acne like I had never seen before!).

Anyway, all the best with it. Let us know how it goes.