My discharge is yellow and smells like baby formula i've been checked at planned parenthood for bacteria and yeast and there was none. what is this?

Trichomonas?: Despite the negative tests so far, this still sounds like an infection. Colored vaginal discharge (yellow etc) suggests certain infections, e.g. STDs; and odor suggests bacterial vaginosis, an overgrowth of mostly normal bacteria. Get rechecked, including a DNA test for trichomonas. Trich causes colored discharge + odor and often missed on usual testing by examining discharge under a microscope.