Progesterone shot

Ladies I need your advice! I went back to my fertility doctor to start the process of IUI after a very irregular period ( we are talking day and half) and he gave me a progesterone shot to start another period. I am suppose to start taking my clomid again on day 2. No problem been through clomid process before however i started spotting two days ago and I am only having real light bleeding. I called my doctors office to see if this is my so called period and they said it could be or it could be the progesterone playing tricks on my body. Has anyone ever experienced this before. I am nervous I'm going to miss my window to start clomid.