You have left many important details out but the answer is almost certainly that's it's not possible for you to get French citizenship easily.
There is something called “effet collectif” of French citizenship that does allow children younger than 18 to get French citizenship when one of their parent becomes French but to benefit from this disposition, you must be named on the décret de naturalisation (or in the relevant decision if your father became French by déclaration). It can't be done after the fact and if your father did not mention you when he applied for citizenship, then you can't avail yourself of this provision.
There is one exception for children who lived in France with the relevant parent for five years prior to the application (having lived in France legally for five years is usually one of the requirement for naturalisation anyway). In that case, it is possible to apply for naturalisation later, even if you weren't mentioned in the décret or decision pertaining to your father's citizenship. This is presumably not your case and, even if it was, you would probably need your father's cooperation to establish that you did really live together at the time.