Lung pain when laying propped up with a pillow

So I have had Covid twice and after the first time I developed it I noticed when I lay in bed on my back with my body slightly propped up I get a horrible sharp pain in my lungs when I try to breath deep. I don’t struggle with it outside of this position but I just find it really odd and I’m wondering if it’s like from damaged lung tissue but like I said I don’t get any lung pain outside of when I lay down on my back propped up. Covid wasn’t super bad for me just felt like the flu and I’ve gotten many lung X-rays since then that are clear so I don’t know what this could be from. I’m also 23 years old and have never smoked or vaped!