What is wrong with my eight month old?

My baby is eight months old and has recently started cutting teeth. She has had a loss of appetite and vomited the last couple of days. Today, I noticed her back had red spots all over it. We continued checking and found the red spots on her chest, neck, and legs. She has also been cranky which is very unlike her. She is generally a very happy baby. Does anyone have any insight on what might be going on? Is it chicken pox? Or could the red spots be an allergic reaction to some juice we gave her. (Gerber Apple Cherry juice)