One of America's most famous bike racers once said, "It doesn't get easier; you just go faster!" And you are seeing that.

Several suggestions: Leg massages, perhaps with one of those massage sticks. I haven't used them, but I used to race and learned good deep massage years ago. Don't ride the same pace every day. Include some deliberately easier days. This includes going up that hill. Be sure you are riding at a high enough RPM. Riding at RPMs of say 60 to 70 is setting yourself up for what you describe. Sticking to 90 - 100 is far easier on the muscles and as good or better for your cardiovascular fitness. (You may find that you want some form of foot retention as you pick up your pedal RPM if you are not already using it. Toeclips or clipless pedals and shoes or platforms with the pins.)

Congratulations for sticking it 'till now. Try some of these suggestions. Keep riding. It will get faster, better, maybe hurt less depending on the speed thing and for sure: more fun.

Ben