You can't switch from an LLC to an S-Corp. They are different things. An LLC is a legal entity (found on the state level). An S-Corporation is a tax entity (found on the federal level). You have both a legal entity and a tax entity. It's possible to be an LLC taxed as an S-Corporation.
By LLC and your usage of the word "my", I assume your tax entity was a sole proprietorship. All of the income/loss that the business earned before incorporating is taxed the same as if it was your own personal income/loss. When you incorporated, you transferred your personal assets (cash, etc) to the corporation. I assume you are the sole shareholder? Now any net income that the corporation earns is passed through to you and taxed as if it was your personal income. If the corporation suffers a loss, those losses also pass through to you and you are able to deduct them as losses on your personal tax returns. However, you are not able to deduct more losses than the assets you had at risk.
If the corporation makes more non-dividend distributions to you than you had invested into the business, after accounting for any business gains/losses, then those excess distributions are taxed as capital gains.
