Natasha, you shouldn't be taking a prescription drug without being monitored by your doctor, so if you think the joint pain and stiffness is an allergic reaction, and you think you know what it is a reaction to--you should be talking to your doctor, or at least your advice nurse. The medical professional who prescribed the medication (you didn't say what it was, so I can only assume you looked it up and confirmed that your symptoms can be an allergic reaction to that specific drug) has a responsibility to deal with ill effects of her/his medical care. There also may be a simple way for you to mitigate the effects more quickly, or there may be a risk of damage you are NOT aware of that should be checked out sooner rather than later. Don't take chances with a reaction to a medication that is only permitted to be taken while under a doctor's care.
Even if the effects have passed, or become less difficult, I hope you have or will consult(ed) with the prescribing doctor to be sure you haven't sustained some kind of damage you don't know about (yet.)