I had Juvederm on my cheeks. One side is swollen and painful. Is this normal?

Having swelling, soreness and bruising is not impossible. These are all " Normal" side effects after injections into the cheeks.  Give the product 2 weeks to settle and the swelling and bruising to subside.  If for any reason you are concerned you should go back to the doctor who injected you for an assessment.

I am sorry to hear that you are having a problem.  You did not mention when you were treated and that is an important piece of information.  On the basis of your symptoms I do feel that you should be evaluated promptly by a physician with expertise in injectable fillers.  If for whatever reason your injecting physician is not able to see you I would seek another opinion. 

With any cosmetic procedure there is a possibility of complications and nothing is ever considered "impossible". I advice you to have an in-office follow up with the physician that preformed your Juvederm injection. If this physician does not want to have a follow-up with you and you feel like something is wrong then seek out a second opinion from a highly qualified board certified physician to address your concerns. Good luck to you