My heart has been skipping beats for 3 days?

I'm 16 5'5 and 108 pounds, my heart used to occasionally skip a beat i'd be fine. I started taking fish oil to get a better heart rate in may. A few weeks ago my heart was skipping beats when i laid down and breathed in for 2 hours, now its doing it when i sit down or lay down and breathe in, its been doing it for 3 days and its making me so nervous it feels like my heart has an extra beat (i heard thats what a skipped heart beat is) thats the only symptom i have and my heart rate is 84 if that matters. I went to the doctor last week for the time my heart was beating weird for 2 hours and he said my blood test (it was only a finger prick tho) and blood pressure are fine (105/68). What could be causing it? I'm pretty lazy i just have a fast metabolism so thats why I'm thinner, i was told to exercise but the thing is ever since two weeks ago I've been taking more steps and walking a lot more than i usually do (my iPhone tells me how many i takes) i have been eating bad though… I'm just really scared and nervous. Could it be caused by fish oil? Like i mentioned my heart used to skip a beat occasionally and the fish oil actually made it go away and now they stay days btw i do have anxiety but this started when i was completely relaxed for once.

Added (1). to better describe the feeling: there's two types of it one feels like my heart stops for a few seconds then beats really hard, the other is when i breathe in deep my heart beats faster and if i feel my heart it feels like there's an extra beat

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Not sure what that would be and I'd like to know too cuz I had my own experiences. Back in late high school to college days, my heart evolved into having extra beats, sometimes it'd stop then have a harder beat and at times it beats faster from normal to abnormal, slow down again and would beat harder and faster. Seems like a roller coaster. But it didn't hurt at all and I was told it's about the palpitation and it might be hereditary. I also remember having daily intake of caffeine, crazy at it is, but at 1st grade until early college days. I get too freakin nervous and that could be causing it too. The only reason it stopped was when I retired from caffeine (but drank in moderation) and I took working out seriously and I still am til today. But now i'm feeling something cuz of road rage and stress at work. Trying to manage it but hoping it wouldnt worsen.