PageRank and Search Engine Position are not the same.
For example: Websites with PR0 can sometimes get more organic traffic than websites with PR3.
Maybe your website does not have good internal SEO, and/or maybe you need to post a few more QUALITY back links to improve the keyword performance of the keywords that you are targeting.
I would be happy to take a moment to evaluate your website to see if I can find any problems or concerns.
What is the domain name of your website?