Why cant i be happy?? Help?

It seems like no matter what i do or whatever happens in my life, im never completely happy.
Just recently i started dating this guy, and hes really good to me but idk. Theres something always in the back of my mind telling me not to get too carried away, dont trust him completely yet and all this other crap.

Im not sure if its anxiety or paranoia or something else but im just not sure how to deal with it.
Im so used to being told "youre not good enough" or "you could be better" or something along those lines.
So used to my mom talking down to me no matter what i do to try and make things better.

Somehow i always let the stress of my past get the better of me...and theni lose what makes me happy.
I dont wana lose it this time. Help?

Thanks guyz.
Love ya.