Karina - I cannot determine what might be causing this from what you've told me, but let's see if we can narrow it down.
My initial thoughts were a food intolerance or allergy.
Other issues may be the sudden increase in large amounts of fiber. If you increase fiber without also increasing water intake, it can cause a "backup" or constipation. You don't have to share with me if you're not comfortable, but how are your bowel movements? Prior to consuming NutriBlasts, did your diet include many high fiber foods like fruits, veggies, or grains? What ingredients are you using in your NutriBlast (liquid included)? Are you rotating your greens or are you consuming the same recipes each day?