Most often headaches are caused by dehydration. Apart from overheating and sweating while in your wetsuit, as a diver you breath dry filtered air which dehydrates you over time.
Make sure you drink plenty of water before and after dives, also best if you don’t have a big night of drinking the evening before and get a good nights rest. There are plenty of other reasons but this is the most common.
I would have never thought about getting headaches Alva so I am glad that you brought this up. I typically do not get enough water in my diet to begin with, so I will have to make sure that if I am going to dive, I do have the water intake that I need.