I've had chest back pain for 5 days saw doctor said I was fine so what could be the issue?

It could be from the anxiety of the pandemic.

Indigestion probably

There's heart burn and trapped wind,the latter can be particularly painful.

Peppermint oil capsules or tea if you like the taste.

Apple cider vinegar diluted before meals

Diaphragm breathing excersise

Chewing food properly with mouth closed

Avoid spicy and processed foods

If you're female, or even male with certain conditions, maybe your breasts aren't getting good support.
Or it could be your shoes. My legs and back hurt but improved when I added arch support to my shoes.