IC design to amplify from microvolt to volt for making a comparator
I'm not sure if this is reasonably possible with your process, but a few things to consider:
AC coupling is a must, in order to eliminate your varying offset.
And you need to go one step further, and produce a fairly narrow bandpass filter which includes 1 MHz. If you produce a DC-coupled amplifier with a 1k ohm input impedance and a 1 MHz bandwidth, you'll get an absolute minimum input noise of 4 uV RMS. Since this is random noise, there is no actual upper limit on amplitude of individual noise spikes, but a common rule of thumb is that noise pk-pk is at least 10 times the RMS value. And the problem gets worse with increasing input resistance.
Fortunately, 1 MHz is a high-enough frequency that you might be able to produce on-chip filters - but be aware that your density is going to be awful, since the area required to produce the capacitors needed will be much, much greater than your transistors. I'd be inclined to suggest that you do your filter components off-chip. And 1 MHz is not so high that things like lead parasitics will give you fits.