I strongly feel that I am adopted
I am an Indian
The things that concern me are mostly the behavioral differences of me and my parents, I am quite open minded and quite a spender
But my parents are misers, they are narrow minded and none of their thoughts match mine
I am quite a [B]obese type guy, but my parents are thin
And I don't look like any of them, in the sense of facial structure
I don't have much, or I should rather say any photographs of my childhood
The only reason that I don't ask them is the fear that WHAT IF I AM NOT ADOPTED?
That would hurt them. Also they favor my elder sister in every decision and never listens to me(this case is generally a reverse in other families), my dad is such a prick, he keeps on scolding me whole day long( I am a 17+ year old boy)
And the last thing that concerns me is the age difference between me and my elder sister(who is 17 years older than me!!!)and conditions are getting worsened day by day and my dad keeps on threatening me to throw me out of the house as soon as I turn 18
Please someone help me by giving suggestions on what I should do to clarify my origin... :(

1) Ask your parents
2) get a copy of your birth certificate
3) get DNA testing

Lots of children go through a phase where they feel they might be adopted. The vast majority of them are not.

Here's a thought: maybe your sister is your mother.
Sorry.
I think you are being silly. If you are a big spender at 17, where are you getting money? Who pays for the roof over your head and food and clothes and internet and school?
That to my mind puts me on your parents' side, and if your father kicks you out at 18, he's not being a bad parent. He's teaching you responsibility for your future.

It seems to me that you might want to focus on yourself more for your own problems, rather than trying to find a reason for them- i.e. blame the parents- as many 17 year olds would do.

I agree- put the adoption issue to rest. Let's assume you are theirs.
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If you don't like who you are, do something about it. Find less fault with your parents, and figure out what part of the poor relationship you have with them, is your responsibility. If it has reached the point where your father wants to throw you out- maybe you can make a list as to what those reasons might be?

Can you be critical of yourself, and show that level of maturity, in helping to determine why you are the way you are- without blaming your parents?

Things you take for granted as Joy said- food, shelter, clothing, etc. will come to haunt you as you grow up, because you'll look back and hopefully realize and appreciate all that they did for you, while you were disrespecting, ungrateful, and selfish in return.

If you don't contribute to the financial stability of the family, you have zero say in how your parents manage their money. It is THEIR money- not yours. Calling your father a 'prick' and 'narrow minded', is completely disrespectful in their home- and you're worried about them not being your parents because they are not like you?

I'd say that's a good thing you aren't.

You lost me when you called your father a "prick." In fact, I can't believe that got through the AMHD censors.

Your family probably treats you the way it does based on your disrespect toward them.

If you want better treatment get a job, get a apartment, make your own way in life.