There are blood test that can test for Metal Sensivitity ( as Medical people like to refer it to). One is called Lymphocyte Transformation Test and Lymphokine Migration Inhibition Factor Test. Check out this article from Medscape: http://emedicine.medscape.com/article/1230696-overview#aw2aab6b4
It sure can be an allergy to Titanium. Read all the others who are allergic to Titanium:
Click here: Allergic to titanium? - Allergy - MedHelp
It is important you know that most orthopedic metal implants are metal alloys, containing more than one type of metal. In addition to the titanium which is present as the base metal, there are other metals that are present in smaller quantities, such as nickel,aluminium which could be present.
About 10-15%of people are allergic to nickel, which could be present in the orthopedic implants.
It's advised that you see your doctor, who might have it replaced with an implant that has no nickel, however there has to be conclusive reports as to what metals you actually react to.
Take care.