First step find a pediatric ophthalmologist at www.aapos.org and get him fully examined including pupil dilation. DO NOT have neuroimaging like a brain MRI until after this appointment. Yarrow is correct that the eyeglasses pain and the "blacking out" symptoms may very well not be related. Conversely the headache could definitely be due to going without glasses. Your son is reading himself into being more nearsighted. This happens and it's too late to stop it. Children with nearsighted parents are more susceptible.
I'm not a doctor, but I have been a parent and I'm sure you are pretty worried about this, so I'm responding now.
If I understand correctly, you are saying that your son has recurrent headaches, that he does not see well even with glasses (which he doesn't like to wear) that were recently corrected again for astigmatism, and that now he gets some kind of visual effect when he moves his head quickly.
First of all, have his eyes been thoroughly examined, complete with dilation and a good look at the retina? Did the eye doctor say everything in there was healthy?
I ask because recurrent headaches and a sudden blackening field of vision such as you describe are not necessarily related to problems with glasses or lens corrections. Frankly, if your son's eyes have been found to be normal, I'd recommend taking your son to the pediatrician or a pediatric neurologist for an opinion regarding other medical causes for the symptoms.