I been trying to get pregnant already for 3 years and when i finally did i had a miscarriage why if i have every month normal periods what's wrong???

Low progesterone : I am not sure how you are defining a "normal" period. It should be approximately every 28 days, last 3-5 days, have a medium flow, no clots/cramps/spotting, no PMS. You may not be producing enough progesterone (pro gestational hormone) during the luteal phase (2 weeks before starting your period). Make an appointment with your OB/GYN and get check