Okay try this, it sucks, but GHI limits your options.

1) Take out your GHI book and start calling the primary care physicians to see if any of them are atheletes, you may get lucky.
2) GHI should okay a total phycical, but you may not get all the tests you want
3) Lower back, would be an Orthopedic issue, so you need that specialty, Not sure if you can do that
on your own or you need a referral from the primary with GHI.
4) Muscle development sounds like you need the gym. Find one and go to Mens Health or Mens Fitness
for a workout program AFTER you find out your back is okay.

Your back is most likely from your weight, but you did not mention your height. Biking upright will be better than in a "road" position but ask the MD.

Try posting on 5bbc.org and nycc.org also in the Northeast forum here.

Claudette Lajam is a member of NYCC club and an Orthopedist in Forest Hills, she is a Cyclist and "may" take GHI.

Good Luck

Rob