Peanut's ears were both up when he was about 3 months old, then they fell back down when he was about 4 months old. I found out later that to help keep their ears up you have to shave the top 1/3 of the ears, inside and out and keep them that way. The groomer actually shaved them all the way down the first time, and they popped right up! I would recommend having the tips shaved sooner rather than later just to make sure that they will stay up.
Hope this helps!
Congrats on your new baby!! SOOOO cute!!