If you feel that you are still a bit under inflated, it is certainly reasonable to have more added as you see fit. It does not have to wait more than a few weeks after treatment to allow for swelling to subside first.
Juvederm usually lasts between 6-12 months depending where you inject it. In the lips its closer to 6 months. If you are not satisfied with the results of 1cc you may have more put it at any time. There is no reason to wait if you are not happy with the results so far.
Once the effects from your last Juvederm treatment has resolved, you may then discuss the option of another treatment with your cosmetic surgeon.
The beauty of Juvaderm and most of the injectable fillers is that there really is no minimum time that you have to wait between treatments. You could literally have injections done every week until you are happy with the results. At this point you should be able to go in for a re-evaluation and any areas that you feel like you'd like to be fuller can and should be injected for you.
If you had your injections in December and go back in for more this month, they may not totally wear off at the same time but it is such as gradual process that it is nothing to be concerned with.
There is no set interval between Juvederm application to the lips. If 6 weeks has passed and the patient wants more, and it is a reasonable request, then it is fine to pursue more Juvederm. The end point and intervals are dictated by the patient and a reasonable plan. My Best, Dr C
It is not a problem to add more filler to your lip even after a few weeks. Discuss with your practitioner that you would like your lips fuller but don't want to wait until December!
Go ahead and haste more filler placed in your lips to achieve the look you desire. Only go slowly in many visits to be careful..