To my eyes you sound stressed because you have a lot of irritating things going on at present, and your workload has increased: but you haven't got a new routine or been able to delegate anything. You are also working harder, but there is scant reward atm.
One problem is that routine household matters need time, effort and thought, even when you have more important things to do (a fact that never seems to feature in time management books) .
So: you do need a specific slot for your former Monday afternoon jobs ? it looks like a 3 hour slot? Otherwise, revert to the old routine and find a 3 hour slot for study, or three sets of 1 hour slots, or similar.
Or see if any of that can be delegated, or reworked ? eg, someone might need to babysit for an hour while you work.
It seems almost as if that slot was keeping your stress levels down and now you don't have that, so it's pretty important.
Next thought: take proper breaks while you study/work, and do it before you snap! Pretend you're having your statutory 15 minutes tea break.
If you can go outside and take a ten minute walk, better still.
But you also need another adult to hand sometimes. You can't be expected to study, work, run a home and keep children safe and entertained without a bit of support now and then. Can you swap favours with a friend, call on a relative, buy in help with anything at all ?. What could you suggest to a friend of yours in your position? Your partner is an obvious source of support, but don't want to press that if you're not happy with the idea.