ANDY'S ANSWER: If feeling blue is a new thing for you, then yes, it could be your changing hormones. On the other hand, everyone's life sucks sometimes. As you become an adult, there are more pressures in your life. You are expected to behave in a more mature manner, and start taking more responsibility for yourself.
Instead of everything being about having fun, people (especially adults) start having serious expectations of you to start behaving with more thought to the future regarding your education, and how you are going to start looking after yourself and be on your own.
Peers seem to also have a new set of expectations and sometimes it's difficult to figure out what will make them happy with you from one day to the next. Consequently, you are juggling what your peers want of you and what the adults in your life want, not to mention trying to figure out what YOU want for your life. Sometimes all those things conflict.
All I can tell you is that sometimes you have to take the time to assess how you're feeling and try not to over-react. Being hormonal is not a good excuse to behave badly. Try and find some things you can do to help you feel better when you're feeling low, like indulging in a hot bath, or relaxing with a good book and a cup of hot chocolate. Sometimes getting a bit of fresh air and exercise can do wonders for your frame of mind, while giving you some time alone to think.
Another trick that works for me when I'm feeling down, is to do something nice for someone else, especially if it is anonymous and I know that person could use the help. There is just something about doing a random act of kindness that is good for the soul.
As far as your weight is concerned, it totally depends on your height and bone structure. Your doctor can tell you if you are in the normal range of where you should be.
Below is the recording of Andy answering this question.