[escape_thereal_world]

It could be anything. Periods are definitely rarely the same from month to month. They can be late, missed, or just weird due to stress (good or bad), change in diet, change in exercise, change in sleep, etc.

So, I would say it's nothing to worry about right now. If you have another strange period next month, or miss it, I suggest a doctor. But it's likely nothing to worry about.

Also, if the brown was at the start of the period but it got brighter and more red a few days later, it could just be old blood from your last period.