You're making good, steady progress. The stairs will continue to get easier. Just don't let anyone try to rush you or tell you that you should be doing better. They haven't had a knee replacement and they don't understand that it is very major surgery. As Legin said, you look normal, so other people have no idea that healing is still taking place.
It's almost 5 months since I had my knee replacement and I still have some difficulty with stairs, if the treads are too high. Smaller steps are easier.