K.W.
I wish I could help you. I feel I have been helped by the responses here. My problem is my dd wakes up to nurse, same as normal, but after 1/2 hour or so (depends if I have fallen asleep) I notice she is sleeping. I try to get her to stop sucking and she either wakes up right then or as I lay her back down. She has ended up in bed with me several nights now. Can't help it, I can't stay awake, I'm exhausted.
Have also noticed she is a lot more fussy during the day, we are thinking teething. But after reading other responses I think I will keep a diary of what I eat and what she eats, see if there is any food intolerance issue. Her feces have changed, but at first we figured she had gotten the same bug I had, diarrhea etc. Now I realize maybe I need to watch what she eats. She is so picky, has only been eating jarred baby food and I can't get her to eat hardly any homemade food. I bought a magic bullet because I thought the baby food grinder wasn't getting it fine enough. Still no go. But maybe what I have gotten her to eat is what is bothering her. Will have to check. You mentioned the flailing and the arching, I just thought dd was showing her temper, maybe she is in pain?
I still don't get in your situation why things seemed to go better and then go back worse.
I hope things get better for you.