How should I approach my hair loss

[biolittle]

I'm 18 and at the very beginning stage of my hairloss. The hair on my hairline has thinned out a little and I have had some recession. Also some of the hairs on my mid scalp and vertex have become frayier and less manageable. I would be fine with my hair if I stop it from getting worse. At the recomendation of my dermatologist I have been using rogaine foam on my hairline for about two weeks and I just started using it on my entire head. Because I still pretty much have a full head of long hair its hard to apply rogaine to my entire scalp. Does anyone know a good way to apply so i can cover my entire head. I am slightly considering taking propecia but the sexual side effects make me really hesitant and I waiting to see if the rogaine works. If anyone has any general suggestions as to the rogaine, propecia or how I should attack my hairloss in general it would be much appreciated if you helped me out. I'm hoping to stop it where it is or if im lucky thicken the thinning hairs and regrow the few i've lost.
looking for guidance,
tom