You would have to prove that the doctor violated the standard of care. This means you'd have to prove that a reasonable doctor in the same circumstances would have given the diagnosis sooner. Then you would have to prove that the delay actually caused you harm. For example, if your condition significantly worsened in that time and would have been preventable had you treated it right away, you might be able to show cause.
I am not licensed in IL and can offer you general advice. In making a negligence claim, you can recover only those damages associated with the negligent act. If there are not damages associated with the two month delay, there are no damages to recover. There are very few conditions that would be significantly worsened by a two month delay, and you would need to obtain expert testimony to support your claim for damages.
Did the delay cause you any damages? If you have a condition for which prompt attention was required, and because of the delay, you now have a worse prognosis, you might have a case.
Keep in mind that medical malpractice cases are very expensive. Unless the delay in diagnosis has or will cause your grevious harm (such as your death or horrible disability), you likely don't have sufficent damages to jusfity an attorney taking the case.
