[MooseSuite]

Check the shower drain connection, run your shower into a pail, do you have a leak? Check your cold and hot water connections. Shut off the hot water, run your shower into a pail.
If all ok then check cold water connection.
I assume you have a external shower head, joined at the water connections. Check this connection when checking the hot water connection.

If you have a Fiberglas shower stall check for hair line cracks on the floor. Seal with epoxy.

I posted this, website shut me down, so near a duplicate answer, but I'll leave this,