Ulcer & Menses

I realised that I will always get mouth ulcer right after menses. I wonder why? I drink a lot of water. Maybe I lack vitamin C. Even with them, I will still have one or two ulcers. Could it be due to hormonal change? Or maybe the body temperature increases during ovulation. Then my body become heaty that causes the ulcer. Whatever it is, I am going to stuff my body with as much Vit C as possible, drink lotsa water and also drink some cooling drinks to lower my body temperature. Then wait and see whether got ulcer or not after my next menses.