Why am i Confused when i talk with Girls?

My name is Nader & i'am 18 years old, i'am living in Egypt, I am not looking as i'am 18 years old at all, Anyone who see me just keeps telling me you'r 15 years old, i'am slim , I'am only 43 Kilos Weight, i'am not Short, i've got a problem that keeps me Confused, i hope you help me with it. My mom passed away while i was at the age of 10, i just mentioned that because i believe it's the main reason for my problem. My problem is that i've never been able to talk with girls like the way i used to talk & deal with boys, when i was in school, i could never talk with girls ,i feel that they are the only Persons on Earth that would understand me, however , i'am now in second year in collage. Things Changed to more Confusing. When a Girl ask me about anything , I just answer her & smile. I 'am Trying to be as much kind as i can because i Came up with a Conclusion that Most of Girls are Sensitive , That's the Main reason why i want to have a Girl friend. , Girls in my Collage Came up with a conclusion that Nader(me) is a very Polite & Calm Boy. that when i & my class mates Play with each other by group , they Treat me as if they'r feeling sorry for me, i still don't know how to talk with girls but however they seems to be knowing me already without even talking with them , but i believe that's not enough, my problem is like this "when me & all my class mates are sitting in the bus for example , I just Plug in the Headphones, or Play with my PSP or anything like that, i just don't talk a lot,. Whenever anyone of them Try to talk with me about something , i just don't know how to reply back , i think they might believe that i replied rude, or as a joke, i get Confused,. I stated my Mom's death because i just want to know if this have any influence on me. I would be VERY Pleased if you guys could help me & i would appreciate it more than anything. Thank you in advance.