Suggest Treatment For Chronic Headache

I went to one eye clinic and they gave me a prescription of 1.50 and 1.75. I could see perfectly out of these glasses but I had chronic headaches everytime I wore them, which was only for distance reading. I went back to the Sam clinic and he said allergies were to blame for the headaches. Dissatisfied with this answer I decided to go to another eye clinic. They said that the reason for the headaches was due to my prescription being to low. Now the prescription is in the 3s. I got my new glasses and the pain in my eyes were so intense I could barely walk. I know an adjustment period is needed for every pair of glasses but why did my other glasses not cause such disoretnation considering I never wore glasses for my entire life until then? So was my other prescription correct? And what is the cause of the headaches?