I hit my foot and when i stand up it starts getting swollen and hurts alot. what could it be?

A hit foot: Sounds like when you hit your foot, it caused a contusion that is affecting the blood vessels and causes swelling when you stand up and gravity naturally pushes fluid into the area, which is having trouble flowing out from the contused area. The resultant swelling in the closed space of your foot then pushes on the nerve fibers causing a pain reaction. Rest it, elevate it, try nsaid, see your Dr,

See your doctor: and have it checked as you could have a fracture, a contusion.....

Did you post before?: If you were the one who posted before and said you still had severe pain often after 5 days, then, if so, you might need an x-ray. If it hurts to bear weight more than with other mild injuries don't walk on it, use crutches, and if it is no better with ice and elevation after a 3 days, and it still hurts to bear even a little bit of weight, get x-rays