Is being thirsty a pregnancy symptom?

YES! It definitely is. Your body needs to increase your blood volume by up to 50% during pregnancy. A 30% increase happens in the first trimester (big jump!), making that the time of the most dramatic change in blood volume. I drank and drank and was STILL thirsty for a good portion of my first trimester. You may also feel quite tired, as the liquid portion of your blood (the plasma) increases more quickly than your body can make new blood cells, s.a. hemoglobin. As a result, you may experience a sort of anemic response, which is also totally normal and okay in early pregnancy. Later on your blood cells will catch up, and - if not - your doctor may prescribe an iron supplement.