That is an excellent question, and based upon the minimal history provided, I think the best medical advice would be from your primary care doctor
who will best be able to obtain a detailed history and physical examination and discuss with you the chances of getting an STD
while using a condom during sex. What I can tell you is that the chances are very low, but not at all 0% of getting an STD from sexual intercourse with a condom. Sometimes condoms can break and this can cause transmission of sexual fluids that can lead to STD transmission. When you discuss this with your primary care doctor, you should tell him or her what the concerns are that you have regarding why you are worried about contracting an STD. Do you have multiple sexual partners or are you having sexual intercourse with people that have a high risk for STDs (such as prostitutes)? These are all very important things to tell your doctor as he or she will be able to counsel you on the best course of action and discuss with you whether you are engaging in risky sexual behaviors and also whether there is anything else concerning that might be going on.