Ovulation/trigger shot w/ several mature follicles..?

Ok. My husband and I have seeing a fertility dr. for about 8 months now..I am taking shots for ovulation however i normally ovulate on my own..we went in for our ultrasound yesterday morning and are scheduled for our IUI tomorrow..When they did the ultrasound they found 6 mature follicles between 15-19 in size..I administered my HCG trigger shot last night..I have been cramping off and on since before the shot last night..could my body be naturally going through ovulation on its own or is it possibly just pre ovulation cramping..I am worried that i may be ovulating before they do the iui and it wont take..we cant bd tonight because my husband has to save his for tomorrows iui..if anyone has experienced this i would like to hear your stories..thank you..