In 2006 I was convicted with a drug charge. I'm now 21, and can't get into the college I want because of this charge. I know very little about the inner workings of the legal system. Any VALID information would be appreciated.

In the US a past felony on your record does not stop you from going to college, so why have they denied you admission? Some of the better private schools, have limited enrollment so there is often 2 or 3 people applying for any one open spot, so you will need to pick a JR college or a public college where this will not be a issue.

If you are talking about getting loans or grants, that is different, In the US, many of the funds for college is not possible if you have drug charges.

Since this happened when you were?? What 15 ?
It should have been done as a minor, in Juv court, and those records are sealed ( in the US)
But even expunged or sealed records are not always sealed from other government agencies.