In my experience, going from 5mg to 3mg is a bit of a jump.  Any changes made by my doctor have been in 0.5mg increments over several weeks.  Probably the first and most recognizeable change will be in your overall energy level.  I find when my pm dose is too low it’s very hard for me to get up and get moving in the morning.  In these instances I feel like I can sleep forever and I feel really run-down in the afternoon (very sluggish).

Additional hair growth is probably the last symptom you will see, and once the hair is there, it’s there.  Bloodwork in 3 weeks of a dose change is probably a good idea in order to avoid any permanent changes (ie: facial hair).