'Nacrez' progesterone only .. 12 days early HELP !!

Ab
I take the progesterone only pill and came off on the 30th April. I missed a pill last Thursday and have started bleeding yesterday ????? It's a 'proper ' period. Do u think it's because I missed a pill or something else? I'm not having sex so I know it's not anything pregnancy related. Any tips or advice ladies ????