Hello /r/fitness. Pretty casual gym-goer here. I've been in decent shape throughout most of my life, including now. But my friend noticed something strange after I was complaining that my right side of the body sometimes feels stronger: my left pectorialis seems to be somewhat underdeveloped compared to the right one.

It's not very noticable from the front, but when I raise my arms straight up it is definitely visible. Pic attached, excuse the armpits: https://imgur.com/a/6e26bCW

I was wondering where this could have developed, as this noticably affects my bench press and other chest exercises.

Would be great if anyone could suggest how I could fix this, or if this is not the pecs but something else. Thank you!