I've had issues with my first rib getting out of alignment, but it presents as pain in my upper back, almost my neck, a bit to the side of my spine, almost to my shoulder blade. It's pretty painful and often comes on pretty abruptly. I haven't experienced any discomfort anywhere in my chest due to the ribs slipping, though.
What I've experienced has been easily remedied with an adjustment from my chiropractor, but when I was seeing a PT for shoulder issues she also showed me how to work on that rib area using a sheet, applying some tension while tilting your head and stretching. I couldn't possibly describe what to do without pictures, but I'm sure your PT will be able to help if this is what is troubling you.
Getting a tennis ball and placing it between myself and the wall and rolling around on it in that precisely uncomfortable spot has provided some relief when I can't get to the chiropractor quickly.
Hope you find relief quickly!