Why is the water in my faucets just lukewarm and not hot?

I tried changing the thermostat and no luck

*note*
Didn't see the thermostat post until after I posted, you obviously have some idea what you're doing. My guess is the element is corroded; they become deposited with minerals from the water and become far less efficient over time. You have to drain the tank but it's not a hard job. I think they are like $10-$20 to replace.
You may just need to adjust your water heater if it's a new place.
Careful not to burn yourself.
Look for a panel on the front/bottom of w/heater, remove with screwdriver.
Find a small dial (mine has temperatures listed on it), it may/probably has insulation covering it, pull this out to access dial.
Turn to the right in small increments, with screwdriver.
Enjoy your hot water, unless heater (element) is bad.