There is no way to know what your site's Pagerank is. The Google PR toolbar is obsolete and Google doesn't disclose what their Pagerank algorithm really is. We know that backlinks contribute to Pagerank, but we don't know the details. Therefore, you have no way of really knowing if your site is increasing or decreasing in PR value.
Remember, PageRank is just one factor in Google's ranking algorithm.
In order to gain pr, then there are many factors for the same such as your web site should be search engine and user friendly.Apart from this your web site should have quality, relevance, and high pr do follow back links.
Google updates the page rank to all the websites over the web only once in 2-3 months, wait for the next update and build some backlinks, also add a google +1 button in your website because PR is now also dependent on how much +1's your website have.