The distinction between organic and inorganic carbon compounds, while useful in organizing the vast subject of chemistry... is somewhat arbitrary. Organic chemistry is the science concerned with all aspects of organic compounds. Organic synthesis is the methodology of their preparation.
No, it is not possible to contract the typical STDs, such as syphilis, gonorrhea, chlamydia, hepatitis B, etc. from wearing someone else's dirty underwear. However crabs and scabies, may be spread in this fashion.
A. Yes. If you have engaged in unprotected oral, vaginal, or anal sex, getting tested for STDs is important. Although many STD infections do not show symptoms, it is still possible to spread them. Getting tested will put you at ease and help you begin any needed treatment.