i agree with Dani boi
you need to break up ur muscle groups to ensure u really give them a good smashing then a have a good week to repair
For example my schedual is:
Monday: chest and tri
Tues: Legs/abs
Wednesday: upper back and Bi's
Thurs: Shoulders/abs
Friday: lower back ie Deadlifts and back extensions
To be honest mate training 3 days a week might be ok to start with but soon enough u will plateau as ur body gets used to it:
You say u have a fast metabilism, personally i think people use this as an excuse for not growing:
For example i left school at 17 years old to join the army, i would eat ok as i was still living at home and i wieghed in at 69kgs
after the first 6 months of just eating properly i put on 10kg. since then ive really concentrated on getting bigger by eating everything and anything, and along with training ive hit a peak of 91kg, im now 22.
I wouldnt say i have great genetics either
Main points
train hard
eat often (at least every 3 hours) especially before and straight after training
maintain a constant sleeping patterns 8-10hours
You should get some pics up as well so u can keep a track
take some measurements every 3 months to track progress
good luck!!!