It may be that the shower hot water has a LIMITER on it to keep anyone from getting burned as the hot water is just that very hot.
You should be able to take the valve apart and adjust it to a higher temperature. Most domestic shower valves adjust up or down 3 degrees per notch.
If you had hot water before it may just be that dirt is in the valve and reducing the hot water flow. Again open the valve and check.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles