Strategies To Lose Weight Fast

I’m a male, use to be skinny bc i was a runner but then started working out. I’m still slim but muscular, but my neck has gotten thicker and i would like it to match my body and since im not buff, i would rather it be slimmer. Everyone says it looks normal but i have a minor issue with it, so any advice would be great.
does it make a difference that I use whey protein after my workouts?