What's your rotation like? Are you making sure to keep both diseases up on both targets with as close to 100% uptime as possible? Are you burning off B runes on Blood Boil? Are you opening up with DnD?
Also you really should have Epidemic as Blood.
On a final note, you can try replacing Glyph of Plague Strike with Glyph of DnD or Glyph of Death Strike, both of which are more optimal for Blood tanking IMO.