Recently starting drinking coffee w/stevia & milk in a.M. Why do I start yawning 30-45 min after coffee? Also, feel dizzy. Not dehydrated. Sleep ok.

Not sure. Are you using any other medications, drugs, alcohol, or herbs? Adding milk may slightly affect the phenols (antioxidants) you get from coffee, but the content of caffeine that increases alertness should be the same. Stevia isn't known to cause tiredness or yawning. Tiredness, depression, or boredom may lead to yawning, though.