Sorry some of you have had a bad Sunday 
I posted earlier on the thread that there are some really useful info and exercise videos on YT about costochondritis, and definitely, iirc, one of the prods you can do yourself to see if it might be that is pressing the tissue where the sternum meets the ribs.
I think it's something quite common, and more likely to be so this past year when we all sit hunched over screens and not getting as much day to day upright movement as we should.
Martha- have you had a h.pylori test? I had h.pylori infection about 15 years ago and my symptoms were like yours, kind of constant gastritis burning. My GP was sure it was my gallbladder then, and I went for a scan/tests no issues anywhere except slightly elevated liver results. It was h.pylori.
Ironically I have the gallbladder issues now, but spent ages googling h.pylori again (among many things) to see if it comes back.
My gallbladder issues go right down into my groin (hence me initially going to gynae for private groin/gynae scan) The more I read the more I understand, misbehaving bile can cause all manner of things you'd never imagine.
Headaches- I get everything (migraine, sinus and that one that starts in your neck and kind of moves up and over) but oddly I never worry about brains, I'm too busy prodding fatty bits! I think the up and over one with me almost feels like it's the bones and fluid between bones and tissues in my neck and head if that makes any sense? When I get it if I move my head everything clicks and creaks. 