Hi, I'm 23 Years Old And Not Sexually Active. I

Hi, I'm 23 years old and not sexually active. I have irregular periods which have a cycle of more than 30 days normally and which lasts for about 7 days but this time I got my period within 12 days of my last period. Also my last period which was as stated 12 days before my current one had lasted for 4-5 days only.
I can't figure out why is this even happening with me. Also except for irregular cycles and stomach ache lasting a few hours I have never had any problems with my menses. Please help!