Your personality will change! But you definitely want to be consciously guiding those changes or else who knows what you might end up with. It sounds like you could definitely benefit from counseling, but I also think a lot of young adults go through the existential dramas you are experiencing and if you choose to tackle these things on your own please be prepared to be patient. The best advice I can give is to pay attention to what your emotions are pointing to and take the time to get to know yourself. I can only speak to my personal experience, but I always had existential questions and struggles from the time I was very young and the best solace I found from that was taking the time to explore that - looking into spiritual disciplines that resonated with me, learning about the science of consciousness, whatever calls to you. If I've learned anything from going back and forth with therapy and self help, it's that it needs to be a meaningful journey in order for it to change anything. That doesn't have to mean religion, but the existential issues don't go away without some serious soul searching - and that can take a lifetime. If you're having short-term issues that are having a direct impact on your life, I would suggest therapy. They can give you a lot of coping skills to get you started down the right path and can at least explore the nature of your problems to figure out if they are more existential or are indicative of mental illness.

Whatever direction(s) your path takes you, wishing you luck and light!