Trust me Alexa is the worst possible ranking system you can rely on.
Anyways the PR is just a nomination to sell better links on your blog or site thats all.
And backlinks help you get the PR up in no time.
Anyways try to post your posts in various high PR forums and also try to post some articles regarding your blog in some article submission sites and give your blog link for a back link. They provide the best back links that can ever be possible