Hi, I had my medical about 3 weeks ago. There is a great chance that you are vacinated for the TB. Most countries still vacinate. If you have no proof of vacination they (doctor) will give you a skin test that will come up positive from the vacine anyway. After that you'll need to go back for an X-ray to show the doctor that you're not really sick with TB, but vacinated. Thats what I did.
I dont know if you did that the first time you got your medicals. If you didnt to be on the safe side, go and re-take the medical exams, or just show proof of that X-ray, or vacination if required on the interview.
After the medical the doctor gives you a sealed envelope that you need to mail to the USCIS office thats handeling your case. In my case I had to send it with my application.
Good Luck!