What Causes Frequent Headaches On Taking Accutane?

I have been taking Accutane, (Isotretinoin) for roughly a month now. I started on 20mg, and I was recently bumped up to 40mg. I have been getting headaches more frequently, and more intense since the change in dose. On 20mg, I did feel some pressure, but with the 40mg for about 4 days now, I have been feeling alot of pressure in my head, almost as if someone was filling my head up with a bicycle pump. When I move around it hurts worse, especially if I am subjected to light, or if I stand up (orthostatic hypertension type of thing)... but its just chronic... What should I do.??