I think your site is in initial stage of promotion so your site keyword ranking fluctuate. To improve and make the keyword ranking stable continue the off page work.
it takes time and boosting kws needs more work than and effort, patience is needed in duration of 1-3 months you should see the progress and if not then something isnt enough or wrong
Keywords seem to fluctuate often there is nothing new here and this can be expected. But your site should remain in the first page no matter what and how much the keyword fluctuates. Only then can you survive what Google has to throw at you.
Keep building links as long as your diversify. The worst thing you can do right now is stop building links. It should come soon. It's probably a google dance.
Google uses several different data centers that have different rankings, and they are switching your version of Google between different data centers.
Everyone struggles to get their keywords on top pages of search engines, competition is very high and even Google algorithms are very complex to understand. Do not stick to one or two particular keywords, check for other keywords which you are not concentrating, but still some where they are ranking, use those keywords as a base to get concentrated keywords in good position. Dont too too much of directory submissions, social bookmarkings it may lead to overoptimization.
Have a check on the backlinks that you have recently created for the keywords that you are working on. Spammy links are not going to work. Concentrate on getting content based links on a regular basis for keeping the keyword position intact.
It's just Google dance that is taking place. Your site is pretty new. Wait for sometime to see stabilized keywords