GERD - look into it. I have it, I had horrible chest pain and it would increase my heart rate when it was its worst. Gastroesophageal reflux disease. If you haven't already and they told you it is not heart related, check that out. But secondly, don't be satisfied with one opinion saying it is not your heart, you never know with more opinions as to what it could be. -especially with the pain in your arm.
Does the pain in your chest ever feel like a burning sensation? Ibuprofen or any kind of anti-inflamm can irritate it:
Nonsteroidal anti-inflammatory drugs include aspirin, ibuprofen (Motrin, Advil, Nuprin) and naproxen (Aleve). They are commonly associated with causing peptic ulcers, and also may cause GERD or increase the severity of symptoms in people who already have GERD. Research has shown that long-term NSAID users were twice as likely to have GERD symptoms as non-NSAID users.
Other reasons I thought of GERD right away is because you mentioned how you noticed it was right after you eat and then lay down - certain foods can be very bad if you have acid reflux and over stuffing yourself can irritate as well:
Avoid lying down for 3 hours after a meal.
Gravity helps to keep the stomach juices from backing up into the esophagus. Lying down with a full stomach makes reflux more likely.
Raise the head of your bed
With the head higher than the stomach, gravity helps reduce this pressure. You can elevate your head in a couple of ways. You can place bricks, blocks or anything that's sturdy securely under the legs at the head of your bed to raise it 6 to 8 inches. A foam wedge under the mattress can also be used. You can also use a wedge pillow to elevate your shoulders and head.
Just my thoughts, but like I said, don't eliminate possibilities until your intuition tells you to! ! good luck