Let’s set up a basic difference between an STI and an STD. An STI is an infection that you get if you’re having unprotected sex. When that infection starts to show symptoms, it becomes an STD. In any case, both are nasty and you can pass it on to someone else.
The problem with STDs is that they may take a long time to show symptoms but the infection, STI, could still be passed. You or your partner may look healthy with no signs but the virus, bacteria, or parasites, maybe very well inside your system. Like with HIV, you can appear healthy for about a decade without showing any symptoms!
The best way to know for sure is getting tested.
When treated early, most STDs are easily curable. Remember, it’s never too late and a condom is a must!