Frequent Periods, Prolonged Heavy Bleeding, Unprotected Sex With Different Partners. Morning After Pills Taken, Clear Vaginal Discharge. Treatment?

Hi, I am 16 years old from the UK and I am experiencing very frequent periods, once a week usually, and they are very heavy every time and last for up to 7 days. I often feel very stressed and down and have no energy to do anything in life. I ve been to see the doctor and she gave me a blood test and suggested that I go on the Pill . I am sexually active, having had unprotected sex with people who have had sex beforeand I ve taken the morning after pill on 3 occasions. I told my doctor I m not sexually active as I was with my mum and I felt embarrassed so I just said no, but I sometimes get a lot of discharge between periods, nothing unusual; it is thin and clear/white and has no bad smell but there is a lot of it and I m not sure if that s normal. I was slightly worried I may have an STD and I m really scared I don t know what to do without having to tell my mum, because that s really not an option she would be disappointed that I lied and think differently of me. Please could you offer some advice to what I should do and what my problem may be? Thank you.