Hi...Skin conditions are best diagnosed only after seeing directly. I suggest you to upload photographs of the same on this website, so that I can guide you scientifically.
The sleep disturbance could be due to the itchiness of the
rash which she is experiencing.
Spitting up of milk and arching of back are signs of gestroesophageal reflux.
The stiffening is called Sandifer's syndrome and in this they arch their back so much to avoid recurrent reflux and aspiration into the lungs. Your daughter will need -
1. Antireflux therapy -
Proton pump inhibitors + antiemetics
2. Always make her lie down in a propped up position - as in the care seat. She should not be sleeping completely flatly.
3. Avoid heavy feeding and feeding more times and in small aliquots.
You can approach me at the following link.
Once the page opens there will be an option below my image as – ASK ME A QUESTION – click on it.
Please find the link below -
www.healthcaremagic.com/doctors/dr-sumanth-amperayani/67696
Regards - Dr. Sumanth