Do i have an STD Syphilis?

I had unprotected first time and only time in 2003, after 3 months i had a std test which came clear, (relived), but these days thinking about it has got me paranoid, first of all i only ever had once , does that mean my chances are less of catching any stds? second of all as i said i had a urine test and was clear and was also told by the health officials its very unlikey i will get anything as usually the high risk are s or africans/west indians, also the fact i only ever did it once, but after when i had that 2003 i got ill like a fever few times, could have been from stressing out, but i never ever had any phsycal signs of this and its 5 years on, so am i clean u ppl reckon? by the way i cant take a blood test for specific reasons.