Pain under breast radiating to upper back?

[Polarbearflavour]

Any ideas on this welcome! I have booked a GP appointment for Friday...

For the past 3 days I’ve been walking up around 5am with a stabbing type pain under my left boob/in between boobs. This radiates to my upper back. Only co-codamol seems to relieve it. Pain is around 7/10.

It then reoccurs a little throughout the day but less painful.

I was thinking pleurisy or Costochondritis?

It could be excess stomach acid or 'gastritis'. It gets worse when the stomach is empty. You might notice it getting better after food, then worse again maybe before dinner if your stomach has been empty for a few hours. It's irritation of the stomach lining. The pain can go through to your back.
Your GP will help.

When my MIL had a pain similar to this, though slightly more central, it was gall stones.

I had similar. It was gallstones.

Thank you! Will see what GP says.

My GP agrees with you! I’ve been referred for an ultrasound scan and had bloods done. I also have a short supply of Omeprazole.

That's good. If it is gallstones then it's easily fixed. Keyhole day surgery to whip it out and job's a goodun.