Is it heartburn? Gassiness? Or something else ?

Upper stomach around the triangle there felt uncomfortable and felt abit tightness n slight pain till chest area when deep breath in while sitting down. Honestly its kinda hard also to explain the feeling of it. Its ok when lying down but when sitting down can feel like a pressure or slight tightness till around chest there. Like about to be breathless but not 😵‍💫. Any mummies experience it? Currently at 25 weeks now. Got it quite a few time. I got no medical history so far. Can advise