Period changes-I’m confused

Hello all. Got my first period when i was 12. It was always very heavy with blood cloths and lasted a week each month. I would need night time pads to not leak but still leaked sometimes. Was never painful, all i had was tiredness around my period, never cramps. However, things have changed and i want to know if someone else had a similar experience and why they had it. From last year my periods got SO much lighter. They started to decrease in flow and days. 6 days, 5 days, 4 days. Around may of this year my period was EXTREMELY light. It lasted 3 days and I did not fill a normal size pad in a day. It was very odd. The last 3 periods have lasted around 6 days. 1st day being very light, 2nd and 3rd day bleeding most (3 normal size pads in a day which is not heavy) and then 4th and 5th day i will not bleed any at night, bleed light flow in the morning, stop for hours and bleed again light flow etc. 6th day is just very light brown spotting. (I am now 15)

What could be causing these changes? I am a little confused about this and i want to know if anyone else experienced the same thing and why it happened to them. I want to know if it is normal. I will mention that I am a virgin, i was never on any form of birth control and i always had regular cycles. Feel free to ask me any questions. Thank you for anyone who read this and will leave me a comment.