Yes, clomid can cause problems with the cervical fluid. It is an anti-estrogen that works by attaching to estrogen receptors in the brain, tricking the brain into thinking there's not enough estrogen so that the brain will send out more FSH to stimulate the ovaries. But, it also attaches to places where the estrogen helps make cervical mucus, so there's less. (hope this makes some kind of sense)
It affects some people in this way more than others. You may want to talk to your dr about it. Doing IUI would be a way around this.
This is a prime example of the way that clomid becomes a contraceptive after 3 to 6 consecutive cycles (FYI, it was originally invented for the purpose of being a contraceptive). It acts in a similar way on the uterine lining.
-eaglet