Hi. It's difficult to feel left out and not being able to feel happy and equally frustrating when people around you are. See a therapist/psychologist as he or she will be able to help you understand as to why you have these crying bouts and such distressful thoughts.  You will go on a journey to understand yourself and your thoughts in a better way. Everything is connected: your emotions, to your thoughts, to your physiology and behaviour. Hence, a change in any one of them will bring a ripple effect to the rest. This will be done with the help of a psychologist. Happiness is a state of mind and can be achieved if you are at peace. Hope this helps.