Hi yixiusky,
Have you connected your Bulk to a suitable potential (Its not clear from Figure) Check each component value (just to be sure its not a chance error, coz sometimes even if you select apply to selected only the first selected device's parameter change).
Hey why isnt there any connection between your Diff amp load's gate and the cmfb load gate? (Atleast not visible in pic).
Was your diffamp tran output proper? What is your supply and expected dc output value?
I think you are using input signal freq either outoff band or it where the gain is dependent on signal amplitude.
zopeon