I had oral sex almost 2 months ago & i i have white stuff on 1 side of throat is it a std? i do have sinusitis or is it post nasal drip?

STD unlikely, but...: If you performed oral sex, it is possible you acquired an STD. But no oral STD is likely to cause symptoms like yours; probably unrelated to that event, most likely just a garden variety cold or post nasal drip. However, if the sex was high risk, e.g. new or unknown partner, or partner likely to have had sex with others, get tested. All sexually active singles need STD testing from time to time.