It's a common problem for every one who start using Reading glasses. You need a period to get use to it. There are some skills can help you.
Use your reading reading glasses only when you need to read something closely. Don't wear that on your ears, put reading glasses closely to the materials.
You may need to modify the distance between the materials and your eyes. Take off reading glasses after reading 30 minutes. Then massage your eyes for a while.
You may feel comfortable with the glasses few weeks later.
Sure, first, only usr them when you need them for reading closely held materials such as a books or newspapers.
Second, put the reading materials at a comfortable distance from your eyes and assess the magnification.
Third, limits your reading time to 20 to 30 minutes
At last, pay attention to the eyestrain with your new reading glasses.