Hi Chayanne
We've just got through the same situation. I'm guessing your son was a dependent and aged out before you took your oath. That happened to me too - took two years and daughter turned 18 before my oath. Ugh!
The GOOD news - she applied under the 5 year rule and her application got processed pretty much immediately. My guess is that because she was on my file up to this point, when her application got picked up they just dealt with it since it was already at the local office.
The 5 year filing was SO simple and quick compared to the 3 year one I kind of wish I'd just waited and done it that way too! She also said that the people at USCIS were really really nice to her - I think they know when they are dealing with very young adults that it's a daunting process.
Also, if you file online, the automated system is not super smart. When you answer yes that you are a citizen it will keep prompting you with popups that your son my already be a citizen. Just ignore it and continue with the application. The system didn't seem to make the correlation between the date I took my oath and my daughter's date of birth, even though I put those both in.