What causes periods to last longer than normal?

My period started 10 days ago. I bled for 4 days (I usually do 5) but now I’ve been having old blood for 6 days which is very not normal for me. It just keeps coming I don’t understandThis has never happened. Is this something to be concerned or just something that happens once In a while? I usually have old blood bleeding for a day maybe 2 max. Waiting for a doc appointment but where I live it’s near impossible to get one.