Clomid and longer luteal phase?

I've taken clomid on cycle days 5-9 the last 2 months. I used to ovulate on day 14 like clockwork. I've been doing the OPK this month and I'm now on cycle day 16 and still haven't gotten a positive LH surge. I had an IUI done on Wednesday, were we too early? Why am I ovulating so late?