Dark spots in the mouth roof- ulcer.

Hello doctor, I am a 28-year-old female. I am a non-smoker and non-drinker. For the past 3–4 days, I have been experiencing mouth ulcer like symptoms. Even mildly spicy food causes burning. My mouth feels dry and sticky, and the left side of my throat feels sore, as if there is an ulcer or some infection. Because of this discomfort, I could not sleep last night. Today morning, I noticed a few dark spots on the roof of my mouth and similar spots inside my cheek. This worried me, so I visited a local hospital. They prescribed Pantoprazole 40 mg, a B-complex tablet, and Zytee gel. Are these dark spots normal? Usually ulcer spots are white or red, so I am concerned about why these are darker in colour. It's NOT cancerous right? Could this be something serious, and what should I do next?Please help!!