not looking at the htaccess code, I leave that for others.
you need to understand that Alexa doesn't know your real traffic, it only guestimates based on people who have their toolbar installed. I highly doubt many of your users will have that toolbar installed, the demographic is highly biased towards web professionals and you're probably the only person who's browsing your site regularly and got one.
Jumps like this are not uncommon if you start browsing your own site less frequently and/or no new regular users with a toolbar arrive on your site - nobody really knows how Alexa actually calculates the traffic.
To sum up, don't sweat over it until you're at least in the top 100,000 (you can start bragging when you're top 10,000), and nobody really cares.