The difference between Knowledge Sharing and Knowledge Management lies in three words - systematic, routine, strategic.
Often this comes from the assumption that "knowledge management" means "the management of knowledge", and that knowledge, being intangible, in incapable of management. We already know this is not a sound reason to avoid the term, as "knowledge management" can also mean "knowledge-centred management" or "management with knowledge as a focus", and there are plenty of intangibles with their own management systems.
Knowledge sharing is also only part of knowledge management, which also includes knowledge seeking, knowledge synthesis, knowledge creation etc.
However there is another difference between the two, a difference which justifies the use of the term "Management", and a difference that can be summed up in three words.
SystematicKnowledge Management should be part of a joined-up system - not relying on ad-hoc use of a tool, or selection from a toolbox, but a systematic approach and the application of a full framework.
RoutineKnowledge Management should be embedded into the routines of work, rather than being an occasional add-on, or something separate. It should be a component of the work cycle.
StrategicKnowledge management should support the business strategy, should focus on strategic business knowledge, and should have a clear line of sight to the strategic business drivers (as in this excellent example from Oxfam).
If you are approaching the way knowledge is created, discussed, shared, synthesised, stored, sought and applied, in this way - systematically, routinely and strategically - then you can justifiably use the word Management to describe what you are doing.