Hi, Wendy! From my 15 months of riding, the answer seems to be "TITS" + patience. TITS is shorthand "Time in the Saddle." You're asking your body to re-formulate herself - you break her down a little each time you ride, and she says, "ay yi yi, I better get stronger if this madness is going to continue" and she does - but it takes time. I think one of the really knowledgable women around here said the rebuild actually takes 2 or more weeks? It sounds like you're doing fantastic!

(Of course, gearing smarts are important for hills. Can't help you there, I'm still in gearing kindergarten.)