Babys neck is bleeding?

My baby is quite the chunker. She gets bad heat rash under her neck. I've tried putting baby powder, A&D, & Destin on it & it doesn't help. Now its so bad its raw & bleeding a little (not much, I have to wipe her neck with a baby wipe to see it.) I've also heard corn starch, vaseline, and Aquaphor can help. I'm doing everything I can to keep it dry & keep her cool. Does anyone know if those things help, or any other ideas? She has a dr appt tomorrow but I want to help make her comfortable til then. Help!