Are you juicing or Blasting? If you are Blasting it could be the higher fiber content of the shakes, are not something your body is use to.
High fiber diets are healthy, but can be hard on the GI tract if you are not use to them. Your body will adjust but I would suggest decreasing some of the higher fiber fruits and veggies in your Blast and focusing on something a bit more basic like romaine lettuce or spinach, strawberries, bananas, handful of almonds and unsweetened almond milk may be a good blend. I would also suggest adding in a 1/2 chunk of ginger to your Blast as this can help with nausea and an upset stomach.