Heart Problems?

For over 4 years now, I've had a problem. I'm a 41 year old male. Every 6 months or so, my upper and part of my middle back starts to ache, like a charlie horse but not as severe. On a pain scale, it rates a 6 out of 10, which isn't severe but very uncomfortable. The pain sometimes goes around to my chest. There is no shortness of breath or sweating, just sometimes a faster heartbeat due to anxiety/fear. No shooting pains down my arm....no other symtoms; just the pain. The pain usually lasts about 5 to 10 minutes. My heart does skip beats every once in a while (3-4 times a day) and then sometimes going months without anything. I've had that problems for about 15 years. The doctor said it was lack of sleep/stress/caffene. I did ask the doctor about the pain the first time it happened over 4 years ago, but he did an x-ray and bloodwork and said he couldn't find anything. Could it be gas causing back pain??? Thanks!