Severe pain after a MRI arthrography on my hip. Take aspirin?

Not unusual. An MRI arthrogram is preformed usually injecting gadolinium and iodinated contrast. One could have allergy reaction to either. Pain after this study is rarely sever. Talk to doctor who did the study. Infection or blood in the joint could produce pain. Rather than taking a pain med do not overlook the possibility of an adverse reaction. If clear for adverse reaction any mild pain medicate is ok.
Yes. Aspirin is a good pain reliever. I'd take 2 three or 4 times a day. You would not want to do this if you have vomited blood or had blood in your stool in the past. Also if you are taking other blood thinners you will not want to take this much aspirin.
Maybe. As long as you have no other contraindication to aspirin, such as a bleeding disorder or certain medicines, then aspirin is ok. Other NSAID medications such as motrin can be used. Narcotics are usually avoided. Assuming that the arthrogram was properly performed, which is not always the case, some patients are sensitive to some of the medicines injected. I also recommend 25 mg Benadryl (diphenhydramine) for pain.