feels as if someone is sitting on my chest?

Pressure on the chest can be caused by heart problems.
However, you don't give us information about your age, sex, occupation, family history, habits, how long the pain lasts, what brings it on, what eases the pain, whether it occurs at night, whether movement affects it, whether eating affects it, etc etc. On page 18 of my book for the laity on Chest Pain When and When Not to Worry (Pelican Publisher, Gretna, LA)I discuss the descriptive language of chest pain - which is pertinent to your question.
To speculate on "what this could be" would be a mistake.
I suggest you consult a doctor about this symptom and be prepared to provide much more information.
Please be aware that I am unable to diagnose medical conditions online.

i also have pain in my chest im 20 year old women. it comes and go's. I guess its not really pain it feels hard to breath as if someone is stepping on me. it has just started sence i had my baby he is now 3 months old so i dont know what it could be.Latly it lasts for a cuple of days and goes away but when its here it scares me. i dont know why it starts but i need to find out how to control it ofr get meds so if you know whhat i should do please help!!!!!!

Anxiety is the cause of every negative 'physical' problem i've encountered.
Hard to breath at night, apnea, heart beat palpatations etc....all from anxiety.
Turns out, it is beacause I can release the anger. This will result in a blank rage where anything could happen with me having no feeling towards it at all.

Everyone said I should deal with the root of the problem, which unfortinately for me, will, HAS to be violence. This is the suppressed emotion which will come out one way or another.
I hope you can understand - you MUST deal with anyone giving you a hard time. If you are not in a profession, violence I promise, will cure you. Not too violent though - just enough.
Matt.

Yea because violence is definitely the solution to anxiety. You will still have the problems that made you anxious in the first place and have more in the end if violence is really how you solve your issues.