I would advise you to give it a bit more time (at least 3-4 months, and preferably 6) for several reasons...
First of all, your breast outcome is probably going to evolve for that period of time, meaning that at present you are likely not seeing the final outcome of your initial operation. It may be that after a suitable period, when you have achieved your final outcome, that you are indeed happy and no longer desire a second procedure.
Secondly, expanding your skin too fast by placing implants, and then larger ones soon after would increase your risk of developing stretch marks or other problems you would I'm sure rather avoid.
Finally, even if you do decide to proceed with an implant exchange, waiting until your outcome is stable and final will make your surgeon's job much easier, and the outcome more predictable.
So while I know you are impatient to get what you want, I think waiting a bit longer would only be in your best interests in that regard.