If you buy more than one item from the same seller in the same week all feedback left of received only increases the feedback score by one. Multiple feedback left in different weeks count separately.
You'll get your stars soon, - first a yellow, but you need a score of 10. When you buy multiples from one seller, it only counts as a single sale in the feedback score. It is set up this way to prevent people from artificially boosting friends feedback scores. They can still do it, but it will take a lot longer. 🙂
Have a look at the following link about how feedback works, - scroll down to where it says how the scores are calculated:
