My lover has had to point this out to me again and again. Most businesses don't break even in their first year. When a business does its considered highly successful.
Amazon and Barnes and Noble makes the risk of self publishing very little for the idea of a very big reward. You can publish your books essentially free. I have spent $12 on my own domain name for a year, and I just completed out my “free trial period” for photos for my covers, I use free design programs so I don't even need to worry about those astronomical prices.
But I fall into the category continually of being upset with my own numbers, saying things like "they were so high last week, why are they low this week?"...which, of course, is bad.
Frankly I don't have enough stats to know the “swing” of the market yet. I was lucky enough to have a few stellar weekends right in the beginning, so when I had a weekend that wasn't so shiny I nearly had a panic attack. I have to tell myself over and over again, DON'T DO THAT!
I've read several people say they go through entire months with half or a quarter of their sells, and honestly it may have nothing to do with you. I have also read about authors that in six months have quit their day job because they're making so much... and that too discourages me.
Over and over my lover reminds me that it will take time to build a fan base, that I need to take things slow, and I look at my steady numbers and am pleased, and hopeful.
Discouragement attacks from many different angles: verbal, sales, blogs of other's success, new policies, writer's block, family, editing, time... Just remember to keep on plugging and give yourself a pat on the back.