I have mine right beside a south window. Looks like you need more light on your ZZ! Eastern and northern exposures are the weakest here in Illinois.

Yes, I would give it more light!

I agree with the above-more light.

It's in a pot that drains, and I water it about once a week (if that).

I would make sure the soil dries completely before watering-once a week may be too often during winter. If the soil remains too moist the the tubers of the ZZ plant under the soil may rot. ZZ plants can cope with dryness well-that's why they have the tubers in the first place (to store water/nutrients). You can use the wooden dowel method to check for dryness-take a wooden dowel (or chopstick), stick it all the way down into the soil, and wait for ten minutes. Afterwards, pull it up. if there is dirt clinging to the wood/the wood feels wet/the wood is dark-colored, then the soil is still moist and does not need any water. If the dowel is clean/dry/light-colored, then the soil is completely dry and you can water.

You can go waaaayyyy more than a week without watering it.