From: Northern NJ, USA
"1. When I plug my headphones into my amp and directly into the theremin I only hear sound from the left ear, is this normal?" - aldenator18
You need a mono to stereo headphone adapter.
2. The pitch range gets smaller everytime I play it and I've had to open it up and tune it a couple times just to get the pitch knob to be in an acceptable range, what's causing this, and can I prevent this from happening?
What kind of Theremin do you have? Is it properly grounded?