When my toilet upstairs gets clogged, which it is doing at least 2x per week now... Once it clogs up , I get a bad leak in the room downstairs under the bathroom shower stall area. I thought it was a problem in the shower stall pipes causing the bad leak, but that was when the toilet was not clogging up, now that it clogs up so often and it leaks , I think it's the toilet causing the leak downstairs... How to I get to the bottom of this and sort this problem out?

You have a leak because the wax seal was never designed to contain water backing up.
The fact that the closet bend loads up with water tells me the problem's not in the toilet itself but downstream from it. The solution would be to pull the toilet and snake the drain line from there. Good luck, Tom