hi, you should really get checked out by your doc - ask to be referred for an endoscopy/gastroscopy (camera down your throat)
however, I had a similar thing when I was about 17 and it was a hiatus hernia - very painful and you can sometimes feel a lump, this is caused by the stomach pushing through a small opening in the diaphragm, which can then cause food to get stuck and stomach acid can reflux - causing the pain/heartburn
http://en.wikipedia.org/wiki/Hiatus_hernia
http://www.patient.co.uk/showdoc/27000867/
You can get loads of drug treatment (over the counter & prescription) to control the pain of the reflux (the hernia itself doesn't cause pain) and in more severe cases, there is an operation to repair the muscle in the diaphragm.
I have had this for almost 15 years and just use tablets to relieve pain.
It could also be reflux oesophogitis - which is just basically just overflowing acid coming back up your gullet - causing the pain (but doesn't explain the lump) - again this can also be controlled with tablets but is also helped by changes to your diet.
Hope this helps
A xXx