I have also met such situation. You could just find the screwdriver to make the arms of the sunglasses be tight. You could stick some bands around the arms to let your side of the head feel comfortable. The ways are so easy. You could have a try to adjust the arms on sunglasses. Then you could feel whether you feel comfortable when wearing the sunglasses.
Well, I have to say that definitely, it will make you feel so uncomfortable if you are wearing a pair of glasses which do not fit you well. So you need to try some ways to adjust them. First, you should put on your eyeglasses and, while looking in the mirror, in that way, you can just identify precisely where the frame problems occur. And then, you can just tighten or replace the screws on your eyeglasses. Finally, you should adjust the arms of the eyeglasses carefully, slowly and gently with your fingers or a pair of needle-nose pliers if necessary. Remember that you need to make a small, corrective bend in one arm at a time. And then repeat it on the other side. Anyway, you need be careful when you do it.
It seems that your sunglasses are not suitable for you. But that is a very common problem we might get, since there are lots of different head sizes, so what I recommend is that you should try to find an optical store and ask the salesperson to help you, they have got the necessary skills and tools to adjust those arms and you could be well satisfied. And then you don't have to buy another pair.