That sounds a lot like my daughter's food allergy... I took her to the dr. and they tried everythinig from bacterial infection to scabies - none of it worked. Finally a nurse said, maybe it's something she's been eating. She prescribed something, but I can't remember what the name of it is (and I'm on the rd. and very sillily forgot it at home), but it cleared it right up. It was like a prescription strength hydrocortizone...
Also, I started watching what I was feeding her. Sure enough, she was allergic to the raspberry jam I'd been putting on her toast (I'd already nixed the PB, thinking it was that. She's not allergic at all to peanuts. It was the jelly).
I'd start watching what she eats... And, it could be exposure to the paint. You can smell the paint, so that means there are particles of it that are airborn. She's breathing those. She may be having an allergic reaction.
If you can afford it, try an allergy test. I wasn't able to afford it, but I sure wish I could!