Hi, years ago, I used to have something almost exactly as you describe. It was on the left side just like you and the pain was about how you describe. I never really figured out what it was, and it lasted for years. It used to really bother me, and it didn't seem like antacids or anything helped. I got it very frequently, and it would really ruin some days out, like if the family and I went out for the day, and I had that, it would just last all day, and kind of ruin the day for me.
I did go for several tests then, and my heart was fine. The symptoms you are describing, like mine, are probably not cardiac. Cardiac symptoms are very specific, and this dosen't fit in with that. Looking back, I suppose it could have been somthing muscular, I was in good shape then also, but maybe just something was getting irritated, or maybe some kind of a digestive thing. Because, I have read where things like hiatel hernia (I am not sure of the spelling there) are on the left side, and can cause that kind of discomfort. I remember one doctor telling me he just thought I might have a 'gas pocket' there. Maybe it's just something like that, that eventually goes away due to your body changing shape, I don't know. I haven't had it at all in the last few years, though. The point is, sometimes these kinds of pains can never be pinned down, there are so many things at work in that part of your body. I did the whole, skip from doctor to doctor thing, and each one had a different opinion, but all just kind of benign explanations. One other one said that I might have inflammed tissues there around my ribs or something, and that can be from anything. Sorry I couldn't help more, I just wanted you to know of my experience, and tell you that it's probably not your heart. Good luck, Val