Progesterone

Hi ladies, I am still just TTC but I thought maybe someone here could help me. I spot dark brown blood through almost my whole luteal phase and it is usually only 8 days long. I am quite sure I am low in progesterone or it just drops too soon. I would like to go on supplements during my luteal phase but my doctor wont give them to me as he says they only give it to women who have multiple miscarriages. I however cant get pregnant if my uterus starts shedding right after I ovulate. any ideas??