Believe in yourself and your writing and be happy and proud of your accomplishment thus far: you are a writer with a published book and people are reading it! If perhaps the sales numbers aren’t what you hoped and it’s hard to maintain focus, as you say, then take stock of what you’ve accomplished, take a deep breath and push forward. You can do this!
Think about the marketing tools you’ve yet to use, or haven’t used recently. What about a new Press Release sent out online, updated with news – perhaps you have a new review to feature or a contest award to announce? No? Then how about entering some contests (everyone loves a winner) or doing a review outreach. Are you connecting with potential readers via social media? Are your pages up to date and active? How about a contest or giveaway via s.m.? Are you blogging and/or guest blogging on sites where your readers may be? Have you done radio? Posted a video book trailer? Content is King (or Queen) and these days so much of marketing is about exposure. Because if few know your book is out there, how can many buy?