Your DA fluctuates over time and you may have gotten hit by Google's "Hummingbird" search engine update.
For links, I'd recommend
1. Posting on forums with your website in the signature line and legitimately respond to questions with good answers, as opposed to spam responses
2. Post new website content to social media with links
3. Take a look at where your competitors are getting links and trying getting a link from the same source
4. Write content for other websites via being a guest host and put a link to your website on the article