The filler chapter nightmare

I love writing when I have something to write. Once a filler chapter is due, I lose all motivation. I don't know how to write things that don't directly affect the plot. Background information, side characters, it's a nightmare. I don't know where to start and if I somehow magically do, I have no idea where I'm going with it and worst of all, for the life of me I cannot make it interesting. I hate writing slow paced shit. Ideas? Advice? Just anything please. I have no idea what I'm doing.