Hi Evelyn,

" I have overflow coming out of my main drain outside (the pipe that sticks up out of the ground)."

That tells me that the blockage is outside your house in the sewer line.
Are you on city sewer or a septic tank?

If you are on city sewer rent a sewer machine,(see image) and send the snake down the open pipe that's overflowing.
If you're on a septic tank open up a inspection port and check to see if the tank needs pumping. Good luck, Tom