For the last few days I have a bad sour taste in my mouth and mild to moderate nausea. What do I do?

Water brash. Sounds like you have some stomach acid refluxing into your throat, which is sometimes called "water brash." if it is mild, it may settle down with otc antacids such as tums, mylanta, and/or pepcid (famotidine). If not improving with otcs or if it lasts for more than 2 weeks on otc meds, see your doctor for further evaluation and prescription treatment.