Hi and welcome
Some periods are slower than others. I suppose I get an allocation of one of my credits once every three days on average. It can be a tad frustrating when you're hoping for that first review, but they do start to come in eventually.
The best tip I've had is to only attach one reading credit at a time. I also think if you do a review, get your credit, and then attach it, it's allocated a bit more quickly. It says somewhere on the site, you're rewarded for doing your assignment quicker. No idea how much quicker this is, but I tend to do it, just in case!
Best of luck
Mo
On turning fact into fiction: African Violet blogpost on Sue Howe's site: http://howesue.wordpress.com/