Hi, in response to your questions, STD's are not always painful.
A hemorrhoid is possible but your description does not make me think this is high on the list. Still, this should be checked for.
Depending on the location of a blocked pore, it may easily be drained or possibly may require a relatively simple procedure to "permanently" open the pore so it does not continue to reaccumulate.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.