33F, sedentary, with a long history of high cholesterol, healthy BMI

My heart has felt weird for a year after a tachycardia episode. I've feel every beat, vibrations/fluttery, chest pain, breathlessness, bruising on my legs, etc. Varying symptoms have occurred but I'll focus on what has been happening lately.
It actually feels 'more' normal lately ( I can ignore my heart if I'm distracted sometimes). But after exercise - it gets worse again for a week or so - so i avoid exercise. At the doctors they don't see anything abnormal so i thought I'd use an Estethescope app to see if it's as they say. I've had it a month. In the day when I'm moving my heart sounds normal (aka at a doc visit). At night or at rest my heart DOES sound abnormal most of the time.

I've started to do some research to self diagnose and I'm taking recordings to show the doctor soon.

I've heard a mid extra beat like sound and a quiet decrescendo murmur from the s1 to s2. s2 is almost always split too that i can't notice audibly but visually. S1 is barely audible. I even heard s4 on some nights (def not s3). The fact that sometimes I don't hear it and sometimes I do is strange to me...

How can the doctors not hear this in the daytime? It can't be that bad if it isn't like that all the time right? I read up on people saying s4 is basically a death sentence within 1-5 years and it has me concerned.

I did have many tests done a year ago and it was all said to be mostly normal and not of concern...but I'm thinking there might be something weird going on here. Thoughts?

How should I go about diagnosing this, as far as my knowledge ecg, stress echo and holters don't rule out every heart condition...what further testing should I do?