OP, I have done my best to help you by deciphering your post:
A very shy girl = Ugly
(I'm a 100% sure) = OP is a virgin
She smiles whenever we see each other = Slightly Retarded
bumps into me "accidentally" = she has an inner ear problem which gives her a Balance Disorder
I've caught her staring at me many times with a mild smile on her face. = Definitely Retarded
I text her, she doesn't reply = 1,She may be deaf and not hear the text, 2,she may have eyesight problems and may not be able to read it, 3,she thinks you are a stalker
Whenever she is online on FB and I start a chat, she goes offline! = she thinks you are a stalker
i just don't understand = we can tell
Has anyone else been through this? = no
When I post updates, upload my pics, 'share' stuff on facebook, she doesn't 'like' = she doesn't like it or you and is ignoring both
others find them very funny and interesting = your MUM doesn't count
she 'likes' the updates of other guys who post stupid stuff = she like the other guys and wants to shag them
This 'liking' thing may be silly and childish, = it is
this issue kinda bothers me. = OP, if you treat it as a numbers game you can get laid by the weekend, go up to and ask as many girls as you can find, out on a date and you will get a date, all this coy bumping into each other is getting you nowhere JUST GO UP TO HER AND ASK HER OUT IF SHE SAYS NO THEN MOVE ON.
God! Women are sooo difficult to understand = you both sound like children