After getting haircut, to my dismay, my hair doesn't look any thicker. Usually the type of haircut does highlight.

Now I'm beginning wonder if I'm shedding more hair than I realize. My diet hasn't changed for last few years, not taking any medication for anything.. Someone commented I should try switching shampoos.

Yes, of course go to doctor with my checkup and ask. After looking at photos of self from over 10-15 years ago, I definitely had thicker hair.
The thing is that I already have a short cut so shedding hair in the bathroom is not going to be a difference that is highly noticeable on the floor.