lump in my throat

First of all, at 14 years young, I seriously doubt you have cancer. It would be very rare and uncommon. The symptoms you describe can be associated with a condition known as dysphagia.

1. Pain or difficulty while swallowing

2. Sensation of food getting stuck in your throat or chest, or behind your breastbone (sternum)

3. Frequent heartburn which could be the heart pain you experience

There are several other symptoms but since you didn't mention others I will leave it at that. 

When you had the x-ray, was it a barium contrast x-ray? Barium contrast gives the best picture of the esophagus. Without the contrast it is more difficult to detect problems. 

Another potential test is an endoscopy. This is a direct physical examination of the throat using an instrument that is inserted into the throat. It’s more invasive but certainly gives the physician a better look at what might be causing the problem. 

There are other tests but these two are the first and will usually find the more common problems associated with dysphagia.  

Probably not. Keep an eye on it and if it gets worse, consider seeing your doctor. It will most likely resolve itself and you won't have to worry anymore.