First you should make sure that you get the right prescription . Check it with your doctor . If there is no problem in your prescription , you may need more time to get used to it . It is common for people to have headache or dizziness in the early use of reading glasses . Allow yourself one week or more to see if it works well .
This is common for most beginners. But one week later, they will get used to them. But if you still suffer from these symptoms after one week later, you may need to visit your eye doctor immediately. There might be something wrong with your eyes or there might be something wrong with your Reading glasses. To most people, the prescription is not suitable for them. As to what caused this, it might be the mistake of optometrist or the optician who screw up everything. But in rare cases, it can be a starting sign of some kind of eye diseases.
I suggest you to have your eyesight checked again because I think there might be something wrong with your eyesight. This time, please have your eyesight checked in the morning than that in the afternoon because the result will be more accurate if we have our eyesight checked in the morning. If there is nothing wrong with your eyes, please bring your reading glasses back to the optical shop where you bought them. The optician will have your glasses checked to see whether they are made according to your prescription. Don't worry. If you get used to your reading glasses a few days later, there is nothing wrong with your eyes and glasses. But usually this will not take a long time to adjust to a pair of new glasses if they are made according to your prescription. Good luck!
Sweetie, are you sure your headaches and dizziness are caused by your reading glasses? If they are a pair of multifocal glasses, I think it is common to suffer from these symptoms for a beginner. But if they are just a pair of regular reading glasses, I don't think they will bring these symptoms unless the prescription on the lenses is not fit for your vision correction. It could be the mistake of optometrist or the optician. You'd better have your eyesight checked again and have your glasses checked immediately. Wearing stronger prescription or weaker prescription is bad for our eyes. We must avoid wearing both of them.