It might be less of a problem with KU but generally I have found that you have to leave time between repeating whatever you found successful. Most say at least 90 days. A FB group for instance has a limited number of people who will down load your book. Unless it is too crowded by authors and your post quickly dissapears, you eventually 'use them up' and have to wait for more to join. Same applies to all forms of book promotion.
I'm Neil from sunny Australia and I write Sword and Sorcery Epic Fantasy set in ancient times and exotic settings, best wishes all!