I don't actually believe that we are seeing more mental health issues in young people, more that they feel more able to talk about them, so that they get more reported
What has changed is the label we've given it and how it is dealt with.
A lot of the way kids feel nowadays doesn't seem much different to how we felt a generation ago. Not feeling comfortable in your boots, knowing where you belonged, being teased (now referred as bullied), feeling your parents don't understand, not knowing what to do in the future and feeling pressured to do well at school by teachers and parents.
The difference I feel is that all the is was considered the normal part of growing up and looking back, that is indeed how I feel. I went through a stage of depression, feeling rejected, not really knowing who I was and feeling nobody understood me. I got over it like most do as we age and get through each stage of youth.
Nowadays though, any feelings that is not one of joy and happiness is considered 'abnormal' and needing a resolution. Nobody should feel sad, pressured, worried, confused and if you do, solutions need to be put in place - by others--to reach a stage of perfect contentment. No kidding kids feel under pressure as it seems they feel they are not allowed to feel anything negative.
The reality is most of us will feel down and negative at times and that's ok because life is full of ups and downs and that's what we should tell our kids rather than automatically taking the approach of 'oh poor you, it's not fair, what can I do to make it better for you', installing a sense of dependence on others rather than growing confidence and resilience in themselves.