Severe penis shrinkage can anyone explain

It started about 3 years ago . My erect penis went fro 4.75 to 3 inches fully erect

Have you put a lot of weight on because that could be the reason if not then the simple fact is you’ve just got a tiny penis 

Have not put weight on I work out 4 to 5 days a week. So it’s not that

Take steroids?

No steroids

How old are you? Take any prescription meds? Other drugs? Smike? Drink alcohol?