Firstly I will answer your question literally- DA (which I presume you mean the 'Domain Authority' metric from Moz) is formulated solely from their determination of the quality, and quantity, of backlinks pointing towards your domain.
If your DA isn't increasing, this is because Moz doesn't deem your backlinks to be of good quality.
- Classified Adverts will not help with SEO.
- Forum posting is spammy, again will not help with SEO.
- Blog commenting is spammy, and it will not help with SEO.
- Social Media is great for getting leads, but all the links are no-follow, (meaning no link juice is passed).
Now to answer your question logically, the DA of your website DOES NOT affect your positioning on Google's search results. Stop the fixation with Moz metrics - they mean nothing!
For now, I'd stop focusing on link building and purely focus on the quality of your website. When you've mastered that, check the forum out for advanced link building methods to get (quality!) backlinks.