I live in Flatsville too, and must either resort to bridges or drive an hour to reach hills. No idea whether or not STP would be reasonable - but I would think you can at least tackle the hill problem by July.

First - USE THY GEARS! Were you doing that? If not, get a feel for shifting down when going up a hill (this is where you'll use your front derailleur a lot more) to where you can keep a decent cadence and rhythm. You'll go faster in a lower gear - really! Then, when you're going downhill, try not to coast too much - gear up as much as you can so that you can get decent speed going down the hill, which will give you momentum (less work needed!) into the next hill. Keep pedaling down the hill, even if it's easy pedaling, because it will help you keep a decent rhythm when you hit the uphill (at least in my limited experience).

Other hints that come to mind - try to keep your heel down as you pedal - you'll get more power out of your push. Also, don't slow your pedaling down as you start to approach the top of the hill - keep pushing hard until you actually crest it.

Your endurance will build with time.

I'm sure those who live in hillier terrain, and who have more experience, will be able to help a lot more.

Good luck!