I have a few suggestions for how you may improve the effectiveness of this deck:
1. Try using cards that come directly from the Orzhov Syndicate (in the return to ravnica block). The majority of the creatures have the
extortion effect, this way you can play your low drop spells and creatures, gain health as well as take health. This way you're not killing yourself with your own black cards.
2. Incorporate more hand hate into this deck.
Mind rot,
black cat,
drainpipe vermin, and my favorite being
slate street ruffian all aid in removing your opponent's hand while also maintaining field presence. Combo this with
shrieking affliction and your opponent will have one
dangerous deck to play against. This would be especially if you drag it out to the late game once you're loaded with mana.
3. Make the deck purely White and Black. If you need lands that sac and fetch lands for you then use
evolving wilds or use
scoured barrens and the Orzhov guildgates. It's less of a strain on your deck, it won't run as slow, and if you add more basic lands then it will move even faster.
4. Lastly incorporate some field control using cards such as
crippling blight,
bone splinters (combo with your
black cat and
drainpipe vermin), and
weight of the underworld to seriously
hinder your opponents. Not that many people have anti-enchantment effects so it would be a good idea to incorporate those into your deck.