How Long Does Penicillin Take To Show Effect On Body?

Hi Doctor I ve gone through a lot of posts over here and thought of asking my question. I ve gone through a medical test recently cause I was due to fly to Qatar and I ve been told that I m VDRL positive and TPHA positive. The medical representative informed me that according to GCC, I m unfit to fly to Qatar and advised me to see my GP. My GP advised me to go to a clinic and get myself thoroughly checked. He advised me to take Penincillin, for three weeks. I took the first shot in my home country and the other two over here in Qatar. The last shot that I took gave me side effects. So, how long it will take for the Penincillin to work on me? Cause I m due to go for medicals over here and when they check my blood test, will it show in my blood. Waiting for your reply Thank You