My girlfriend is lame and really annoying.How can I tell her that without being rude?

We've been together for 5 months and she's just soooo freaking annoying and a loser like really. She's 20 but acts like she's 16 and I'm 23, I'm a freshman in college and shes senior at highschool . . She isn't even concerned about her future, all She's thinking about is living in the moment. The isn't pleasurable at all noooo 4 play at all..I rather use my fleshlight. She act like a little punk and get sad or start crying when I don't wanna talk to her. She's sooo gullible it's ridiculous. Everytime we get in a argument She just agree, which isn't healthy at all it's a lack of communication. She's a diabetic and use that as an excuse for everything. She act like a baby and dont handle up on her responsibilities. She never had a job before and claim She been lookin for one for months. When we talk on the phone at night She sings ALL NIGHT AND TALKS ABOUT NOTHING. When She's talking/ explaining himself she always end the sentence with (or whatever)& her bestfriend is 13. WTF It's like everything was cool in the beginning because she was such a sweetheart and cute & I know everyone isn't perfect but...omg she annoys the crap out of me. like every little thing, and I don't wanna change who she is nor do I wanna sound bossy. How do I tell her without being rude or making him cry