You're pretty young to have heart health issues like this. But shouldn't be discounted just for age. However, remember that physicians take an oath to treat. Have you been to a regular doctor or cardiologist? That's what I'd do. I can't tell specifically what is going on. Physicians take an oath to treat so would not give you the all clear unless they believed that to be the case. However, you still have questions. https://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/sinus_arrhythmia.php A holter monitor may be a good next step.
A picture of your ECGs would be helpful. Your description is too unspecific. It could be nothing or hundreds of different things including your esophagus or big vessels of your heart.