All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
You have to make up all the days that you did not fast, and you should start doing so immediately. As for the expiation, if you did not know that it is forbidden to delay making up for the missed days, as it is apparent from your question, then you are not obliged to expiate for the delay, according to the view of Shaafi'i scholars. However, if you knew that it is forbidden to delay the expiation but you were unable to make up, there is a difference in opinion among the scholars whether or not you must expiate. Nonetheless, it is better for you to expiate, if you are able to do so, in order to be on the safe side.
Allah Knows best.