I got my first job and headaches are killing me

So, I decided to work full tiemp during winter break in order to save some money for college. I work as a cashier standing up for 8 hours, no break brom 4 am to 12pm. The point is that I am getting some horrible headaches, I've always been prone to headaches with climate changes, too cold, too hot or when studying for too long but never for consecutive days. It's hard to focus, I've never been in migraine medication, I only take Tylenol. Any recommendations?

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