check if found specific record then find another record with the same group
try this

SELECT p.TERM, p.Problem_ID,p.problem, PGROUP
FROM Problem_log p
INNER JOIN problem AS s
ON s.problem_id = p.problem_id
WHERE s.PGROUP IN
(
    SELECT PGROUP
    FROM Problem_log
    INNER JOIN problem
    ON Problem_log.problem_id = problem.problem_id
    WHERE Problem_log.PROBLEM_ID = 3
)