Strange heart palpitations with some mild chest pain (but not always). Blood Work + ECG normal. What could be wrong ?

I am a 31 year old healthy guy (Height : 5'6, Weight : 135 lbs) who tries all I can to do everything right with diet and exercise. I am a non-smoker and I drink alcohol occasionally. I do drink coffee twice a day though. I have family history of heart disease.

Since the last few weeks, I have been having these short phases of heart palpitations. They occur every 2-3 days only for a few seconds but during these few seconds, I also experience some mild chest pain. The chest pain is so mild that if I distract my mind from it, I don't even feel it and eventually it goes away.

There are some times during the chest pain that I feel a mild numbness at the tips of a couple of my left hand fingers. I don't feel any dizziness or anything like that.

When I am exercising, I don't feel any discomfort despite my heart rate getting fast. But it happens randomly when I am walking or sitting or just lying down. The other day it happened for a few seconds while I was walking, and I had to stop and sit for a while to feel better.

I got my blood work, thyroid and ECG done. Everything came out normal. On the day of the ECG though, I was feeling great and wasn't feeling any pain or palpitations.

So what else could be going wrong ? Should I even be worried ?

I also must mention that I do get gas-related stomach pains every now and then. Could it just be that I am just feeling the gas moving in my body ?