I agree with the fitting(!!!) and keeping shoulders down, elbows in. Also, I'd add to make sure you are not locking your elbows ("elbows loose" as the pp said). If you do lock elbows, all of the road vibrations will travel up through your arms and into your neck. Keep your elbows slightly bent and fluid. That will also help to make sure you're not scrunching up your shoulders and adding additional neck strain. I think also, as core strength increases and your back and abdominal muscles are supporting your weight rather than your arms, you will see less discomfort. Ultimately, you want your core strength to be such that if someone were to just come along and pull your arms off the bars, you'd barely fall forward because your core strength is your main support on the bike. Being more aero can take time getting used to and some time building the muscles. It sounds like you're doing it right... slow and easy. Good luck and congrats on a new ride!!!