As Fonzie stated, it does sound like you have cold water mixing in on the hot water. I would check the things that he suggested, as they all will allow this situation to happen.
The easiest way to see if the water inside the heater is hot, is to go outside and open the access panel to the water heater. Slowly pull up on the pressure relief valve (shown in pic) to open it up enough for water to flow out... and then you can feel the water coming directly from the heater, to ascertain how hot it is. If it's properly hot here, then you know you must have cold mixing in downline somewhere.......as in the bypass valves being set incorrectly (very common), or either/both of the indoor/outdoor shower valves open, but handheld wands shut off.....as Fonzie pointed out.
Hope this helps you isolate the problem, and please let us know what you find.