I have, very recently, been exactly where you are.
my dds were driving me nuts, lots of shouting on both sides, tempers and emotions escalating, etc.
I dreaded even getting uip in the morning, and lay in bed delaying it for ages.
I used a combination of all the advice already given.
Singing instead of shouting really works. Sing anyhting (even what you would have shouted) to any tune to feel like - it makes such a difference.
Pretending there is someone else in the room sometimes help you not to react in a shouty way. Eg, I wouldn't scream like a fishwife in front of my mil, or my neighbour, so would act as thought they were in the room - it stopped me shouting a few times.
Actually confronting the source of annoyance (the whining toddler) can work too - get down and play for even 5 mins, and peace may be restored. Just one smile form either of my dds can make my day, and help me realise they are not the enemy. they are not here to make my life difficult (even though they do sometimes!) and they would rather not be whining/shouting either (mostly -dd2 can be quite a grumpy little thing at times)
I have, over a few weeks, set myself tiny goals which I have slowly built up.
So getting everyone dressed was the first.
Next, I made sure that each night I read the dds a story at bedtime.
Next I made sure I did a load of washing every 2 days, then every day (still have not cleared backlog )
Tiny, tiny little steps, but life has been a bit easier because of them.
It really is a case of manageing the small stuff - everyhting comes, slowly but surely.
I hope today is a little easier for you.