At the risk of sounding like a 1970's country & western singer, my primary symptom can only be described as a "heart ache".
I have a dull but constant pain just to the left of the lower sternum area. It has been there for on and off for months, usually a couple weeks at a time.
My doctor had blood work done and said that he saw no tell-tale signs (sorry I don't know the specific tests) and I went for an "elevating treadmill" stress test and apparently the machine reached it limit before I did, but there were no signs of a heart condition.
That was 6 months ago. The "heart ache" returned just a couple days ago.
I will see my doctor again but I was hoping that someone here might recognize this as a common symptom of....... something!