H Bridge motor control clarification
M1 and M3 are wired as source followers. This means that the source voltage will be at best 1 to 3 volts below the gate voltage. Given that the gate voltage is 5 volts, the source voltage from M1 and M3 will be at best 4 volts and, under heavy load probably only 1 or 2 volts.

Quite often P channel MOSFETs are used in positions M1 and M3 and you would pull the gate to 0 volts to activate them: -



If you are using N channels MOSFETs in M1 and M3 positions, a bootstrap circuit is normally used that raises significantly the gate driving voltage. Here's a half bridge that uses a bootstrap driver IC: -



Or sometimes, isolated techniques are used like this with 4x N channel devices: -