Weird discomfort on left side of my neck during the day and sharp pain on what feels like my heart when lying on the side. i'm quite young.

Unlikely from heart: Generally, sharp chest pain when lying on your side is unlikely to be due to a heart problem, and discomfort in the neck is usually due to a strain or sprain of the neck muscles. If your symptoms persist see your physician.

Generally, pain that: ...changes with your body position (standing, sitting, lying down) comes from a problem with your skeletal system (muscles, tendons, bones etc.). When a person of any age has symptoms that are strong, last for more than a few days or makes them worried, I recommend they see a doctor. That's my recommendation to you. Best wishes. Dr. Anne