Not sure if anyone has taken clomid before but I have a question..

I just finished my first round Thursday, and I go for my 21 day labs on October 1st. My question is after I have my labs, when do I take my first pregnancy test? My periods have always been so irregular so it never comes at the same time every month.. So not sure if I should even wait until my first missed period.

Also if anyone has taken clomid or knew someone that did, did they have success the first round?