I wouldn't use creatine, unless you are having extreme difficulties in maintaining weight gains. You indicate that you're progressing nicely. Don't use it; it pushes nitrogen cycling hard, and in young growing bodies that already are moving at nearly maximum metabolic rates (max is about 18-19), its not necessary. In your mid-20s, yeah, I would. Don't need it presently..and it would be a little hard on kidneys and liver, considering that you probably already use shakes for protein supplement.
I agree with Double D. Save your money, you won't benefit much from it. Exception would be if you were sedentary and carried a lot of bodyfat before you began weight training. Then, a very small dose might be helpful.