It doesn't seem that a “purple spot” on your tongue is caused by poor blood circulation. Birth control pills don’t affect the blood circulation directly; they indirectly increase the coagulation ability of the blood. Poor blood circulation can contribute to the formation of blood clots. The risk of blood clotting is bigger when women using birth control pills are also smokers and have pre-existing conditions like coronary ischemic disease, venous circulatory failure diseases, hyper-coagulation conditions, etc. That’s why you mustn’t take birth control pills without a gynecologist’s permission. You can seek advice from this health specialist.