Herpes is a sexually transmitted infection which is caused by the herpes virus. It typically causes breakout on the genitals themselves with small fluid filled blisters which are painful or have a burning sensation. When the blisters rupture, the small sores will heal over slowly. After the first herpes infection, the condition can recur from time to time, especially in times of stress or illness
Herpes is primarily transmitted from person to person from direct contact between sexual fluids (like semen and vaginal mucus) and the genitals. Therefore, it is highly unlikely that you could contract herpes from the seat of a toilet.
Of course, you should always exercise proper hygiene when using a bathroom, avoiding dirty stall and washing your hands when you are done. This is more to prevent contamination with feces than it is to prevent herpes or other sexually transmitted infections however.
There are numerous other conditions that could cause itching of the bottom. These could include simply irritation from moisture or friction with clothing. Small red bumps on the bottom are likely to be folliculitis, which are usually minor infections of the hair shafts. This will usually clear up with good skin hygiene.
Please discuss your symptoms with your primary care doctor
for more information.