Is It Safe To Take Clomid Before The Periods Start?

i AM 26 YEARS OLD. i TOOK PROVERA FOR TEN DAYS FROM MAY 1 2011 AND EVEN AFTER ONE WEEK, AFTER STOPPING THE PILL I DID NOT GET PERIODS. DOCTOR ADVISED ME TO TAKE CLOMID AFTER DOING ONE MORE PREGNANCY TEST (IT MUST SHOWS NEGATIVE THEN I CAN TAKE CLOMID). cAN I TAKE CLOMID WITHOUR PERIODS? iS THERE ANY POSSIBILITY FOR PREGNANCY?