3 periods in 1 month!

So, i’ve had my period 3 times this month. it will go away for a week and then randomly come back for 4-5 days, super heavy and clotted as well, and i’ve never had clots before in my life. I’m kind of freaked out. I’m 20, I am not sexually active and haven’t had sex in over 6 months. I was also checked for STI’s last month at the doctors when I went for a checkup and I’m clean. My period is usually 4 days with a normal flow, it either comes on time or sometimes 2 days before or after it’s expected. Has this happened to anyone before? I haven’t made any lifestyle changes or dietary changes so I have absolutely no clue what this could be! Anyone know? Thanks!

OH, i also am not on any form of birth control.