Had normal bleeding until november..since then had a period every 5 days lasting 8 days. help?

HI, I had been taking the yasmin pill for a few months after it been changed due to withdrawal bleeding.. my periods came back regular, decided to come off of it as i am planning for another child with my partner..so i finished the last pack in september. i was so happy to see that my periods were back to normal after having a period at the end of september and october. When it came to november my period came at the end of the month like normal but it lasted for 8 days. Thought nothing of it but then 5 days after finishing this period i came on again (period pains and everything with it) lasting for 8 days. The same thing has been happening up until this present day and would like to know what's wrong with me. I'm only 20 so it cant be menopause. My doctor says its normal but it doesn't feel normal, also been feeling really tired. Pregnancy is also out of the equation. Thank you.