I just turned 19 and male and 5.10 and think I'm still going through puberty. I am still developing body hair (chest and back) for example. as for shaving well can go 3 weeks without shaving and only do shave really when I have to for work other wise I could go a month. some of my friends shave every day and one can grow a full bread within a week. about 2 weeks ago I went to Jersey and was stopped by the police walking though the airport as they thought I had run away from home and didn't look older to fly on my own Also today during my shift at work we were talking about me getting stopped and they said how I didn't look 19 more 16-17. last year went on holiday and lost 3 stone and can not put the weight back on (have been to the dr's they not found anything)when all of my friends are with me it makes me feel down as the size differences between us is huge also within the last few months have noticed the hair on my arms has gone a lot more dark and more noticeable if wearing a T-shirt. is this normal for someone of my age?

also just to add my arms feel really heavy and the muscles are sore and I have no idea why

Thanks for any help