14 week old breaking out in rash

I for the life of me can not figure out what she is reacting to. I do not use scented anything on her. I only use Vaseline. We've tried different baby Laundry soaps and it doesn't seem to be that. She's drooling a lot but I keep her dry as much as possible. I'm not sure if she's teething or what? Could it be teething? Anyone else have this problem?