Yeah you are overdoing it. I would chill out a lot. One thing that's really hard to get through ones head (I know being an ex coke user) is that continually using coke actually makes the drug less effective. I injected cocaine, so I would blow through a gram even faster than someone Insufflating would, but in the end, the results would be the same. I'd get a few good shots at first, and after that I'd just be preventing the inevitable crash-which btw (and as I'm sure you now know) is horrific beyond words.
My advice is to first off, let yourself come down, and then try to stop using (you said you've only been doing this for two months, once a week am I correct?). Obviously if you can binge like this once a week, you will eventually start to do it more often and then run into even more serious problems, so quit while you're ahead.
However, knowing that quitting cocaine isn't easy, I would say, try to restrain yourself if you can, which is nearly impossible with this drug. One way you can do it is to buy less at a time, like one gram instead of five. That way, even if you wind up calling up your connection for another one, it will be a pain in the ass, and you likely won't want to do it again and again (though I suppose I can remember times when I have). I don't know, it's a touch habit to kick man, and you won't be able to function long using like that. I can assure you of this.