Based on the information provided there are three different cause that may lead to the pimple/ bump in the urethra/ labia they are as follow.
1) INFECTED TINY CYST
2) CONTACT ALLERGIES ( like dermatitis
3) GENITAL WART
, getting inflamed due to some reason.
Can't be confirmed with out visual inspection as well as may need some diagnostic test like urine test to find out the culprit.
Please be brave and get your self checked by physician (SAME sex physician will be a better option for shy person)
Here is what they mostly tend to do,
1) Physical examination
2) visual inspection
3) may need urine test in case of infection is suspected to find out the culprit
4) may do some blood test
5) TREATMENT : -
(a) In case of infection/wart mostly respective antibiotics/antiviral
will be prescribe.
(b) In case of cyst, which may lead problem in future, once the infection is treated they might puncture the cyst and remove the content leading to resolve the issue permanently
c) In case of contact allergies , may insist the change of undergarment/ type of protection used by partner may be advised to be checked and anti allergic medication will be prescribe.
So , make sure to visit same sex physician may be any OB/GNY OR FAMILY PHYSICIAN IS OK.
Hope it helps,