The only issue I can think of right off-hand that would make Honor progression slow is continued (if not punishable) misbehavior. Basically, if the IFS flags a report made against you as valid, regardless of whether or not you get punished for it, it can slow or even halt your Honor progress altogether.
However, I'm willing to give the benefit of the doubt, so, maybe light misbehavior isn't the issue. The only things I can think of to help are these:
- If you aren't already, make an effort to spread positivity in your matches. Even if you don't get Honored, being positive helps. (not to mention the obvious of positivity leading to more Honors)
- Be sure to Honor others after each match. Again, even if you don't get Honored yourself, it certainly helps. The Team Honor bonus is definitely not something to skip out on.
- Besides those two, just keep playing, and do your damnedest to win. You'll regain Honor eventually, sooner than some I'm sure, given Riot's recent work on Dishonorable progress.