Know-How Exchange : Social Media

We represent local brands on social media. We have noticed that in the past 3 months on facebook our numbers are suffering. The quality of the posts is getting better every week and we are still losing followers unless we put spend behind the posts/page likes campaign. What can we do to prevent this? Is there a trend on facebook that other brands are seeing? We have 1 brand that we have represented for years that has always shown growth every month and that has slowed since October. The followers are engaged, but we aren't actively gaining new followers. In one case, we are losing followers. How can we combat this? We don't have spend to put behind the brand that is losing followers and they are low engagement in general. What more can we be doing? We already do giveaways and things like that with the products.