I've been thinking about Joshua 1:9 which says:
Have I not commanded you? Be strong and courageous. Do not be frightened, and do not be dismayed, for the LORD your God is with you wherever you go.
This is our 5th year hsing, too and the 2nd year (that I remember) that the first week has been tough. We school year round and last year, dd came down w/ chicken pox on the 2nd day and it was a doozy of a case! This year dd reacted to a medication and had to have Benadryl which knocked her out on the 2nd day. My normally compliant and cheerful 6yo son has been ornery for whatever reason, my husband is out of town for the week, and etc, etc, etc. None of this stuff is major and I am simply refusing to be discouraged or dismayed. I know that Satan is happy to use these things against us, but I am choosing not to let him and just resting the Lord. I choose year round school so that when these things happen, it's not a big deal, so I'm choosing not to make a mountain out of a mole hill!
My 3yo dd is my challenging one. When she was about 20months, I stopped all CM studies, ordered R&S workbooks and handed them to my older dd, b/c that was all I could manage for about 6-8 weeks. I spent those weeks FOCUSED on training the little one and then we were able to return to our regularly scheduled program of CM studies. All that to say, there are seasons when we must settle for less than what our "ideal" homeschool would look like and that's ok. Keep your long-term goals in mind and simply do what you can each day. I've now added a new ds to the mix, but at this point oldest dd can do a lot on her own, so that helps, but I'm well aware that as he approaches toddlerhood, we may have to scale back a bit once again. This time, however, we should be able to keep going w/ our CM studies, just at a slower pace, if need be.
Also, I know what you mean about yelling. I, too, dislike yelling, but this past week, I did so on more than one occasion which prompted apologies from me to the kiddos and a reminder that I, too, must keep watch over the doors of my lips. We all sin and fall short on occasions, but those are often great teachable moments.
Be of good cheer, you are not alone!