It looks a very strange sentence! Where does it come from? The use of 'itself' is odd but the meaning is to emphasise the period of time as a short amount of time to go mad! So the meaning is to emphasis the shortness of the time, but it doesn't look a well written sentence to me.

Hello. When you say a noun (such as a period of time : a day, a few months) + "itself", the word "itself" means "only" or "apart from the rest". Another way to say it would be : Within "only" a few months I had literally gone mad. It means you are only talking about the few months apart from anything that may have happened before that are still affecting the three months but happened a while ago. Another example: "How was your day yesterday?" "The day ITSELF was good. But the day before yesterday I got food poisoning so I felt sick all day." I say "the day itself" because I want you to understand that from waking up to going to sleep yesterday, nothing bad happened. But it was still a bad day because of something that happened the day prior. But since you asked about specifically "yesterday" I refer to yesterday as "the day itself" so you know that I am providing a description apart from anything that didn't take place yesterday. Yesterday only. Yesterday itself was good. Within a few months itself - only within a few months. "Is learning English difficult?" "The language itself is not that complicated.. but understanding all of the aspects of everyday speech is very complex" So hopefully you can see how "itself" if it is the object of a verb means something does an action that reflects back into it. But when itself comes after a noun it means your are talking about that noun specifically, excluding everything else, sort of like the word "only" or "just" or the phrase "apart from everything else"