Maybe it is not even nofap related my friend. Think also about other habits like smoking that can cause it. If it is really strong, maybe it's better to see a doctor
I don't smoke but I relapse recently I spend a lot of time sitting on computer maybe it's a bone injury
Maybe it's also inactivity combined with a bad diet.. But just want to specify, I am not a doctor. So read it just as a simple, altough caring and sincere, opinion.