Ioana,
You have already had your heart checked out and a doctor said it wasn't the cause of the pain and that it was okay.
So we can safely rule out a heart problem.
You have already taken medicine for gas related problems and that didn't seem to help.
So we can probably rule out
acid reflux or a similar affliction.
Sounds to me like you probably have an "idiopathic" (meaning unknown cause) illness called
costochondritis.
Costochondritis is not a serious condition but it is very painful and mimics much of the symptoms of a
heart attack. It is the inflammation of ribcage
cartilage.
I've had it and know exactly how it feels. I once went to the ER thinking that I might be having a heart attack. I didn't. It was costochondritis, which I had had before.
Unfortunately, your bonehead doctor didn't already think of this.
The treatment?
Pamper your body as if you had the flu. Rest, relaxation,
vitamin therapy, and the use of a gentle painkiller like
Advil Liquigel, which contains
ibuprofen - an anti-inflammatory. But use pain killers sparingly and only when sorely needed, as they do nasty things to the body.
The biggest problem with this affliction is that one cannot rest lying down without the pain increasing and preventing sleep. So prop yourself up on a pillow at night or lay back on a recliner and doze when you can. Eventually the pain will subside enough for you to sleep fully.
With improved nutritional supplementation, the episodes of costochondritis have lessened in my life and would do the same for you. I have listed a plethora of nutritional advice in previous answers to questions, so feel free to peruse my responses via my profile.