Update your website content. This time make it more unique, increase the amount of content, maintain a proper keyword density, get backlinks and social media links as many as possible and make sure that they are relevant and of good quality.
may be many other competitors have entered in your niche and are doing a better job than yours. you should try to target the right keywords and should try to get as many backlinks as possible from high pr sites. Also, if you have some articles then try article submission etc. Also do some blog commenting, directory submission etc at regular intervals. (For eg- once a week or so.)
analysis of competitors websites which are ranking in first page on your target keywords. there after post comment using your keywords and URL. get more quality back links to your site.
May be the keywords selected by you are highly competitive....ITS REALLY HARD TO RANK FOR THOSE KEYWORDS... Always opt for keywords that have high search volume but low in competition
Website development actually takes a lot of time and effort. One thing you should forget is that it requires patience as well. Just concentrate on the SEO and content part.
Build quality backlinks. Forum posting is perfect for this if you make LOTS of posts. Always update your content with unique information that interests your users, and include your main keywords when posssible.
In regards to content, better to check your website's content. Maybe it has something to do with it, because as you can see now, there are many sites that have lost their ranking because of duplicate contents. If ever you found some duplicates, update it your site with fresh and unique content as soon as possible.
You could do all of this and if the content on your site is too sparse or it's just copy from somewhere else it's pretty pointless. Write more, create original and informative content, then do all of the above. There's no point doing all the linking if the content isn't worth linking to.