Is it possible to join these both tables?
you can combine them like this, as long as your subse3lect only has onbe row and 1 coumn
SELECT u.*,h.*,d.* ,
(SELECT count(id) FROM OHS 
WHERE Category = 'POLICIES' 
  AND ID NOT IN 
  (
    SELECT OHSID 
    FROM User_OHS 
    WHERE UserID=u.ID AND Type='POLICIES'
  )) as countr
FROM User u
LEFT JOIN HealthDec h ON u.ID = h.EmpId
LEFT JOIN Document d On u.ID = d.UserID;