15M and im a bit scared.

I don't know if this is the right sub for this but for the past week or so, i've been having what seems like palpatitions and it stresses me out. My heart beats very loudly and hard, especially when i stand up or lay down at night, and i feel my heart beting on my neck. Sometimes i feel aching on the heart area or my left arm/shoulder and weakness on the left arm but i don't know if it's psychological. The symptoms do ease off when i take fresh air. Now i would want to go to the doctor, but i already went to the doctor around 4-5 months ago because of palpatitons (but i wasn't experiencing arm aches) and every test came out perfectly fine. Is it possible for a heart disease to occur in between that 4 month time?