Never had a problem with water pressure in our shower started about 3weeks ago
Shower pressure went way down there our no leaks that we know of what can we
Do to get our water pressure back?

I would first check the screen and aerator in the shower head. You have debris getting caught and if its not in the aerator then you may need to open up your mixing valve. Come back if you need help with the mixing valve. Tom, our plumber, is about 2 minutes behind me.