Creativity Problems! Help?!!!!?

So I consider myself artistic but I've always been an observational drawer/painter. I'm creative in the concepts of the idea I want to portray in a piece but when it comes to drawing up a person or the way a certain object looks I can't imagine it in my head. I always have to actually see it to draw it. I'm not talking about copying someone elses work I mean that if i were to draw a tree, I'd have to look at one to draw one. If I don't, and draw it from my imagination it looks wrong. It's really frustrating because I want to expand on being an artist but I feel like it's holding me back. Is there anyway I can get myself out of this hole? I don't want to be like this forever.