How many shots do you get if you tested positive for syphilis and not sure how long you have it?

A single injection of Benzathine penicillin G 2.4 million units IM in a single dose may be curative. Visit this site for information on this topic: https://www.cdc.gov/std/tg2015/syphilis.htm

For syphilis a year or more in duration, or if duration is unknown, the treatment is 3 doses of benzathine penicillin G (Bicillin LA®), 2.4 million units each, once a week. Syphilis of prolonged or unknown duration also requires very careful neurological, ophthalmologic (eye), and otological (ear) evaluations. If any of these are abnormal, you will need 10-14 days of IV penicillin before Bicillin.