constant migraines

You may want to look back through our tongue diagnosis section. A crack down the middle almost to the tip - does not indicate stomach or kidney yin deficiency. A red tongue with no coating and at times -horizontal- cracks (like parched earth) indicates yin deficiency. A crack down the center that goes to the tip indicates either a strong propensity towards mental illness and digestive issues (functionally sp qi deficiency) or both. If it is just through the center it would be digestive issues. The real key there is the coating and their symptoms.

If there are signs of dampness (tongue coating) and weak spleen qi you would not technically want to tonify yin and that would increase the already overburdened fluid systems in the body. Rather you would tonify the spleen and stomach and perhaps move damp.