No gain in CMOS differential amplifier
Your transistor symbols are not placed in a matched manner.
Make them identical, both in the top PChannel? diffpair
and
in the bottom Nchannel? current mirror.
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Also, without I_V plots of the transistors (sweep the Vds 0 to 3 volts; step the gate with 0.1 volt steps from 0v to 1.5v; do for Vbulk_source = 0v, for 1v or 2v) you are only guessing about the FET behaviors.
Also, longer channel devices may be required.