Ok, so your exposure is that you had sex with a girl without a condom, yes?
If so, then that puts you at risk. Is it a high risk? Not the highest but it is definatly a risk all the same.
No discharge at this stage is a good sign, albeit a bit early! The time scales to test are:
Chlamydia - 2 weeks
Gono - 2 weeks
HIV - 4 weeks (4th gen)
Syphilis - 4 to 6 weeks.
It is difficult to say statistically your risk without knowing the whole situation. Is she honest? Is she a friend or a stranger? Those questions to play a part when it comes to "trust" so that is for you decide which route you want to go down in regards to testing or a "see what happens and test on my usual intervals".
If you dont usually test, then using the numbers above, this would be a good time to start.