What I see happening based on your account is that you TRY to write and FAIL, because of fatigue, try and fail, and the discouragement from the series of failures is contributing to your state of dejection.

If you realize that taking Seroquel and working at night are completely mutually exclusive, period, and stop TRYING, you will then stop FAILING, thus stopping to add that extra factor that contributes to the state of dejection.

Writing on Seroquel at night is impossible and you should not try to change that.

The activities your wife performs while off work are, by contrast, alterable. So you both should look at those with an eye to optimization.

Change of activity is by itself rest. If you do stuff around the house and she stays with the toddler when she is off work, you will be happier because the change of activity from taking care of the toddler to doing stuff around the house will be relatively restful for you. Plus, if she is already away from the child for so long while at work, should not she be bonding with the child during those few hours that she is at home anyway??