Periods like to keep you guessing. Because the lining doesn't always separate at a steady pace, you can have a lighter day and then have a heavier one even late in game. Sometimes if you have a chunk of tissue that blocks up the flow out the cervix, you can get a heavier flow again after it passes. As long as your period lasts 3-7 days or so, the day-to-day variations in flow are normal and highlight the need to always be prepared! Don't assume because you are late in your period that all the heavy stuff is done! Bring an extra pad or tampon with you until your period is totally finished.
This is very common. It's happened to me a number of times and every time I think, "Wow, I only had a 2-day period this month!" only to have it start back up the next day. Your period isn't like a faucet that gets turned on once a month; it's your body working out a uterine lining that it isn't going to use and it may do it a little bit differently every time.
I've totally had that happen to me! It's a good thing to keep in mind that there is no normal and every woman is different and even every cycle is different. I wouldn't be too alarmed about your period being "flaky" every once in a while, but there are some medical reasons why a woman might have serious spotting or irregularity. If you want to just clear your head, think about having a conversation with your healthcare professional.