It all looks very good until below his belly button, and for the life of me I cant see his lower abdominal muscle as anything else but a wiener.
You draw alot of ladies, and that is a common problem when swapping from women to men, my only advice is to try these two sites so you can get more familiar with drawing men from the waist down.
https://figurosity.com/ an online site with real and CG models
https://doll-a.net/terawell/ a downloadable app for the pc that lets you customize your model
Good luck!