Ask HN: Question about Contracts

About 18 months ago I started working with a startup, I was 18 at the time. I worked 80-100 hour weeks for no pay and no equity. I signed a contract before I went to college in the fall saying that I was owed $10,000 and 10% of the profits in 2010 (due at the end of the year). I ended up being paid the $10,000 about 8 months late. This summer, I went back and was hired for $6,000 a month. The company ended up making $1,000,000 with ~$400,000 in profit, and when, while in the process of leaving the company to return to school, I asked for the 10% of the profits, they claimed that the contract that I signed for the Summer contained a clause that superseded all previous contracts. My question is, did I sign the previous contract under false pretenses, never intending to sign away my right to the 10% of the previous profits, and is that clause even legal in this case?

It's just incredibly frustrating as a college student who can't afford a lawyer to feel like other people made a ton of money off of my work (I was one of 2 developers, the other ended up leaving and suing for $130,000 for a similar amount of work) and I'm getting screwed. Any help would be appreciated, thanks a lot.