What would cause throbbing that feels like a heart beat in your stomach and should i be worried?

Worry does not help: Throbbing sensation in the stomach could indeed be the heartbeat if associated with fear or anxiety. Talking to your doctor is the best way to get an answer to your question and allay any anxiety you may have. Answers to questions such as these often come from a face to face discussion with your doctor who can assess you more fully.

Aortic pulse: if not associated with pain or shortness of breath, you are feeling your abdominal aortic pulse- it should be the same rate as the pulse in your wrist and neck. It is normal- if painful, get it checked.

Heartbeat: You are probably feeling your abdominal aorta beating which is normal especially if you are thin. You are young and the chances of an aneurysm in it is not likely.