in need of some advice

i’m 15+3 and every now and then i get a severe heavy feeling under my breasts in my chest ? like to the point where i am rolling around like a mad woman trying to do anything to get the heaviness to stop because it feels like i’m dying. i’ve only felt it 3 times so far , the first time i had a really bad upset stomach , the second time i literally felt like i was dying and was about to call the ambulance and then now again this morning. i did have sex this morning and after sex it felt as though my uterus was shoved up into the top part of my tummy and it got quite hard and uncomfortable so i’m not sure if it’s that or what.

i’ve tried lying in different positions , walking , drinking , eating , going poop. walking and moving around i’m learning makes it feel 10x worse. i’m just not sure what to do ? does anyone else ever get this severe heaviness in their ribs ?