What do you think if I'm start to lose myself?
Why would you want to lose yourself?
I've always hated myself compared to my sister who is 5 years younger than me.
I understand you're point, but it's always advisable to get your life in order if you're feeling lost. Otherwise it would lead to serious mental issues.
I just don't know who I am or what I am doing with my life.
You need to appreciate yourself more and love who you are. It's never good to compare yourself to others because you will always compare yourself to those that are in a better situation. Instead, try and see the positives in your life and embrace them.