UPDATE:

I went to the Dr's office and he confirmed that it's a yeast infection due to the area being moist and not drying it well after bathing. Thank you ladies for your comments.

ORIGINAL:

I was giving my daughter a bath and while massaging her with oil I noticed that she has red skin on her armpit, it has a foul smell and it oozes some yellow substance. The same redness was found in the folds of her neck and the skin behind her ears. I'm taking her to the clinic soon, but does anyone have an idea of what this might be? Eczema? Allergic reaction?