Is it normal to not believe people when they say nice stuff *sometimes*

I can take a compliment,
My eyes are a rare shade of green/yellow, this has gotten me a lot of dick in the past *oh hell, what am I saying, lol, past hahahaha* anyways..I have a rosebud mouth...o.k boobs and wavey thick hair that will still be there, even after I'm 70 and should have 2 strands left like Homer Simpson, I used to down on myself a lot, being a heavy-ish chick but shit man, if ya can't deal with your shit and just accept yourself then either make bank and get plastic surgery or stfu already!

Ahem anyways...so I know I've got ok looks physically, SOME talents *can't play guitar too well, and gave up piano* but one thing I NEVER believe people when they tell me is "ugh, you have such a nice singing voice"...I feel my expressions getting out of whack..I feel my eyebrows go up and down uncontrolably, and my half shit eating grin appear and get that whole, like, you're uncomfortable to be in you Own body feeling..my cheeks feel hot, my face flushes out and I just wanna run away...

List of people who have told me I'm good:
100% of my friends, strangers, my mother, random people who have heard me on my karaoke-thing-site..ect

List of people who have told me I suck:
My sister...

NOW!!
It's funny, because that automatically makes it look like I give a shit what she thinks, but on the contrary, I do not, and even if I did, how could I believe her when she thinks her voice is magnificant, when really it sucks and a lot of people have agreed with me.

I don't know what to do, because I love to sing, and when by myself, when i heard my voice, I like the way it sounds, yet I know of a lot of people *Cough American Idol fails cough* who thought they were good, family told them they were good, friends rooted for them and then they get on stage and you're watching at home like "Look at this freakin idiot"...and I'm so scared to be THAT idiot, I don't want to release my soul and so to say break free from what feels like chains, and let `er rip (vocally) if I may get looked at judgementally, or worse..laughed at.

when I turned 21, I didn't look forward to the booze really, I knew there were a bunch of places to do Karaoke, I was psyched, first Bar I went into that had it, I froze, ever since that day, I enjoy watching others and singing along in my head..but I don't even feel like I have a passion for something like that anymore, It doesn't even cross my mind, yet sometimes, I'll go in with a few close friends to play some pool, and it'll be like totes empty, see that microphone and the D.j searchin for new singers and I contemplate it, just for the 3 minute thrill on the stage and sing my heart out, but fear holds me back.

Wanna hear something sad though, in relation to that whole sister thing, She's been telling me I should stfu since I tried out for choir when I was 12, because it was HER thing, and I cared a lil bit of what she though back then, I never sang when she was home, cause I would get yelled at, and YET, now that i thoroughly don't give a shit and almost despise her as a person...when I feel that fear, her face 98% of the time flashes in my head...I mean..wtf is that??

Ok lost my point, eh screw it, unless a psychiatrist posts a comment, don't need anyone guessing about my problems mentally and the hang-ups with sibilings, just wanna know is it normal to be self-conscience about something you enjoy, and also, are there ways of getting over it??