Anything can be found in any age bracket. Just because your 15 - 19 does not make you immune from a STD.
Aids is even possible even though you generally wont know for years to come.
Trichomoniasis is the most common protozoan STD in the US. Aside from giardia, which is rarely sexually transmitted, it's the only protozoan STD.
Chlamydia is the most common bacterial STD in the US, and the most common reportable STD. You should know that not all STDs are reportable, so the CDC doesn't get direct reports about HPV or trichomonas.
Itching
HPV
STD are common in people who are sexually active... if you are sexually active at the age of 20 then you are high risk to have an STD.
STD(mostly)
Nope actually chlamydia and herpes are the more common stds.
The three most common types of Vaginitis are Bacterial, Yeast, Protazoan(Caused By STD's)
50% you welcome
Well I don't know if this was THE most common but one was STD's because there were so many prostitutes following the camps.
Most often they are caused by a common STD called HPV although there can be other causes
Syphylis