What foods act as a natural laxative?

I'm not pooping regularly like I should. Usually every 3-4 days I go, or sometimes I don't go for a week. I really don't think that this is normal, and I'm desperate for ways to make myself poop normally. Please help!
Update: Oh, I forgot to add something else. I eat a lot of fruit and vegetables. Plus, I have 1 cup of coffee a day.
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