Do I need to change my personality in order for people to take me more seriously?

I appear as a very bubby, cheerful person. I'm literally known as the girl who is always happy. If you ask anyone to describe me, thats probably the response you'll get. Truth is though, deep down i'm not really a happy person.. i'm not going to go into my life story here, but my past has been a traumatizing once since birth, and i've always found it easier to smile and keep moving forward, even if deep down I sometimes feel empty. The problem is though, from the pain i've experienced, its actually made me a more compasionate, kind person. People often tell me i'm too nice, and take this as a sign of weakness, not knowing what really lies within me. I sometimes feel that I shouldn't be so nice and so giggly, because it just translates as immature and weak to most people.. even when clearly, it isn't the case. I find many guys i'm interested in write me off quickly because they see me as too sweet and childish, without getting to know me more and realizing that yes I may be sweet, but there is so much more to me than that. I know its awful for anyone to change their personality to such an extent, I mean we are who we are, but would it be better to appear more serious to people in order for them to take me more seriously? I hope my question makes sense.. and i'd really appriciate advice, cause i'm sitting in my room crying now unable to cope with this issue. I've also found that so many people are selfish and insincere, and it hurts me profoundly because i'm always thinking of others and enjoy listening to them and being there for them.. in return, I don't always get the same, so it seems like it would be easier just to be more reserved and cold. As horrible as that is, I feel it will save me the hurt I feel on a daily basis from people who aren't as open hearted. I will stop typing now cause i could literally go on forever but I thank everyone who takes the time to read this and respond.<3