What Causes Pain In My Left Arm?

Hi there, I am a 20 year old man. I have been getting cramping pains in my left arm, as if someone is digging their fingers into my forearm muscle. I also sometimes get a fast heart rate e.g of around 100 for about 30 mins to 1 hour then back to around 80bpm. I am concerned as to whether this is a problem with my heart or whether it could be stress induced. I have had what i thought were a few panic attacks over the past 3-4 months, my Papa died around 8 months ago and since then I have felt like this. I dont smoke a lot, id say around 2-3 a day at most, more at the weekend if I am out. My diet is pretty good and I am active in my day to day life. Could someone please help?!?