Difficulty breathing when lying down

[AmelaL]

Hello!

For at least a year I have experienced the following when I lie down to go to sleep:
1. Pounding heart
2. Heaviness on my chest when lying down on my back
3. Even comforter/bed sheet cover sometimes feels too heavy on my chest if lying down

Little about me:

I am overweight, so I am not sure if this would be due to this problem. I am not a smoker, do not drink alcohol. Mentally when this happens I do not feel stressed out and do not experience any flashbacks. I would not experience heartburn in the moment, though I do have history of heartburn. I do not eat at least two hours before bedtime.
I do not feel out of breath, but it feels like it is difficult to breathe. To get relief, I usually have to lie on my side (left is better than right side).
I sometimes do experience left shoulder pain along with chest pressure. Sometimes, I feel deep burning like pain in the middle of the chest, but it feels different than heartburn. Sometimes, I just experience discomforting pressure in my chest, all over.

What could be causing this? I do not cough.