Yes, it is a valid prenup.1) The law does not require you to have a lawyer for an agreement like this: while you could have retained a lawyer to help you, you chose not to do so. Having chosen to not hire a lawyer, you are held to that choice and cannot use the lack of a lawyer to escape or get out of the agreement.2) Similarly, you chose to sign without financial disclosure. You could have refused to sign--but having chosen to sign without getting all the information that would have been helpful or appropriate, you are held to your choice to sign it. The law does not protect you from your own bad decisions, unfortunately.