@Jeff, you might get some good out of this thread:
The Arch for the Bench Press
Developing the arch through bench pressing has been one of the most significant body changes I've had over the 4 years I've been strength training with kettlebells and barbells.
Funny story, I didn't know how deficient my back muscles were in this particular skill until my husband and I went to watch a Figure and Bodybuilding show. Suffice to say it wasn't my favorite thing, but it was pretty interesting. They would do this pose "from the rear" as the announcer said, arched back and flexed muscles. Attempting to imitate this I found that I had no ability whatsoever to contract my back into an arch. My back could go into an arch passively, such as a yoga cobra or upward dog, but I really couldn't actively contract those muscles to create it.
This skill is unique to the bench press, in almost all kettlebell and barbell movements. In almost everything kettlebell, we are trying to maintain the "canister" -- the diaphragm and pelvic floor parallel, the torso muscles maintaining this alignment and intra-abdominal pressure as we lift, swing, etc. Arching the back is something to be avoided, as is flexing the back. In other barbell movements like squat, deadlift, and press, we are trying to stabilize the spine as much as possible also.
Seems like I can military press with no problem but benching hurts. Maybe I can do light benches on bench day until it doesn’t hurt anymore and then work my way up.
What do you feel, and where? To me it was very uncomfortable at first, and I really had a hard time getting up off the bench after benching. My back was almost in a spasm from trying to so something so unfamiliar. Now, no problem. It just took time. But, maybe you have something different going on.