I am a 17 year old girl 130 pounds who has started to walk/run in the past month. I'll explain my problem as best I can. I feel this semi sharp pain that starts either at my heart or near it and then it goes down the left side of my body slowly like a crowd doing the wave and then starts all over again. This didn't start a month ago but its gotten worse and its starting to irritate me. I told my mom and she just said that its probably growing pains... I don't believe her even though she is a nurse. If anyone has any advice or answers please help me.

Make sure your not overexerting yourself that could be the problem and drink plenty of water after your workout but if problem is still happening see a doctor because this could be warning signs for something bigger also take 10 to 15 min rests between workouts

Are you warming up before your runs? Always make sure you warm up and get your heart working before you run. Do stretches, jumping jacks, JOG in place a bit.

At your age and weight your target heart rate while working out is 142-162 bpm (beats per minute) get a heart rate monitor (they can be found cheap on a step counter) or learn to calculate it yoruself to make sure you stay in this range.

If your heart rate goes beyond 200 while running, its time to start walking for a while.

The same thing happens to me sometimes, but I usually relax over a set amount of time while trying not to think about it and sometimes massaging the area softly, but my heart usually has a longer lasting soft pain, but it might work.