Dealing with Migraines at Work: How to Get Your Boss to Understand

I always get so nervous to call in sick to work with a migraine. My boss gets so upset, not because he's mad, but because I'm one of the hardest workers (I'm not just saying that, bosses have said it themselves), and I'm a people pleaser so I feel really bad. And he almost always blames it on my hours that I've worked that week, which it never it. It almost always is the weather, thats my biggest trigger (I'm a human barometer). I've tried to explain this to him many times but he doesn't seem to get it. And I get it, it must be pretty confusing to an outsider since I don't get them with every weather event but then blame the migraines I do get on the weather. Any advice on how I can get him to understand?