Sak,

The application rules are quite clear.  You are screwed either way.  You either read the rules and lied on your application or you cannot remember when, where, and how many times you used illegal substances.

The FBI is receiving thousands upon thousands of applications for the IA positions.  My advice is to forget about employment with the FBI.  Your acts of youthful indiscretions were not the reason you were disqualified.  You were disqualified because you cannot accurately describe your past drug history.  You should have waited two more years to clear the 10 year history hurdle before applying.

I sincerely doubt that the FBI will consider any future application on your part due to your failure to know your past.

Please know that it is a distinct possibility that the background investigator will contact multiple people that you know back to your 16th birthday if you are less than 28 years old.  The IAs in the FBI will require a Top Secret SCI clearance and they are very particular about it.  If you have any skeletons in the closet, they want to know about it before the press might stumble upon it sometime in your future career with them.

There are many people who have not used drugs that will apply to the FBI.  They will get preference over you, plain and simple.

Regards.