When I first started riding, I was experiencing upper arm, upper back, and shoulder muscle soreness, especially on the right, which went away with riding. That stopped being an issue, but I was getting some discomfort even on short rides in the girly bits. I moved my saddle forward about 3 mm. I did a 36-mile ride this weekend, followed by 15 the following day. No mashed girly bits (except for what I can blame on the chamois), just a bit of sit bone pain. However, I'm now getting the arm/shoulder pain again, plus a little pain in the lower back that gets better once I get off the bike. No upper back pain.

Searching the forums and by process of elimination, I have 4 thoughts:
1) Since I've significantly upped my distance (previously, my longest ride was about 24 miles) after not riding much more than 6 or 8 miles at a time, it could just be fatigue from spending more time than I'm used to on the bike
2) Lack of core strength means I'm putting more weight on my hands than I should. This would seem to mesh with the back pain, but I don't know.
3) Saddle isn't adjusted properly, or is just a poor match. Likely. No girly parts pain, but I'm still moving around a bit to find the right spot.
4) Fit issue. This is possible. I don't feel like I'm rolling or throwing myself forward trying to reach anything--I'd expect pain in other places as well. Nothing feels stretched or numb, just like I've been at the gym and did too much lifting. I don't know enough to diagnose anything, of course.

Thoughts? How would you suggest I go about trying to determine what's going on here? Since I'm short on cash at the moment, I would like to leave the fitting for later if possible.