Technically, אָז is an adverb and not a conjunction, but in action it often connects sentences with the sense “then” and so has been included here. עוֹד, on the other hand, can be either an adverb or conjunction.
Note also that לְמַעַן is originally the word מַעַן with the לְ prefix preposition, and so you may find it parsed in that fashion. But this prefix + word combo is better understood as a single conjunction, just as we saw prepositions לִפְנֵי and מִפְּנֵי.
Finally, you will not see these conjunctions ever possessing prefixes or suffixes. They truly do stand alone.