Chest pain and bloating under sternum and pain in lower abdomen and stomach area

[SWW21]

I am a 15 year old female 120 lbs 5'6" (average) and for all I know I do not have any health issues, though for as long as I can remember I have always had these strange symptoms.
The severity of these symptoms vary (don't know why they are worse sometimes vs. other times)
Though usually I only get one of these "attacks" in the evenings, and sometimes I can go for months without having one, though other times I will have them multiple times a week.
It doesn't seem to be related to my diet, as they can happen before dinner, after dinner, when I am hungary, or when I'm not. Also I eat a very balanced diet as my mom is very concerned with eating a good nutritious diet. [a health freak if you will]

Here are the symptoms:
-back ache/ cramps (shoulder area, upper back, and sometimes lower back)
-severe chest ache (under sternum mostly, though can extend throughout the entire ribcage area on both sides)
               -Definitely an ache [not a burning sensation or piercing pain] which I used to describe as "It feels like there is a rock in my chest" (under sternum area. It just feels like a hard, gripping ache, like someone has there hand in my chest and it trying to pull it out.
-chest bloating (just the chest area swells up and looks like a round ball is in my chest when you look at it in the mirror)
-Sometimes a piercing pain in lower abdomen/stomach area, though not usually

These symptoms can last for 15 minutes to up to 2 hours.
I have discovered that if I sit really (really) still and take (extrememly) shallow breaths that it passes faster and the syptoms (symptoms) do not get as painful
It is usually best to relax my muscles and try not to move at all, so a lot of times I rest (sitting up, not laying down) against a soft couch, or I sit in a chair and lean over in a kind of fetal position [especially when it gets really bed]

There has been one "attack" that I remember to have been REALLY bad, where I was sitting in that fetal position for about two hours, and it got so painful that I felt like I was about to start screaming and tears werre forcing themselves out of my eyes, and my breathing was really erratic (but shallow)
Then I remember after the pain began to fade (about an hour and a half) I was too afraid to get up or move that I sat there and ended up drifting to sleep.