You've got your reps spot on for mass building, so long as you are doing the last one to failure or close to it. If not, you need more weight. (You may already know this stuff, but just trying to help.) It's actually better to have a little more and only be able to do 7 or 8 reps, so long as youre keeping good form.
About adding the 3 pounds in one week, I don't know. You might want to consult or search the internet about that. I know that it's very well possible to gain 3 pounds made (mostly) of straight up muscle.
You're going to love creatine. I'd suggest that you only use it when you get to a plateu, and you've done everything you can do to "shock" your muscles into growth before you go there. (search shocking muscles into growth on some of the meat head forums/sites). Once you've done all of that, follow the cycling instructions to a "T". AMAZING stuff to say the least. I've never done steroids before, but from what those who have done them tell me, creatine is as close to steroids as you can get. I was able to lift heavier, longer, didn't get as sore and fealt pumped for longer. But again, make sure you've gotten to the natural plateu point first, then follow the cycle to a "T". Do this and I personally promise you great results and happiness to follow.
BTW, are you an endoomorph, ectomorph, mesomorph? It's important to know, so you can have a better tailored work out. Judging by the weight you were at, I'd say you are an mesomorph (maybe endomorph). Gaining muscle should be easier for you than most. So love the type of body you have. When it comes to body building, you are blessed!
This may be a good start:
Happy lifting!