Nevertheless I do think it is safe to say that such interjections were used, at least on a day-to-day basis. (Bear in mind that relatively few Old English texts survive to this day and almost certainly not many were produced to begin with. Old Norse itself was for the most part a spoken language, unlike Latin for example, and its predecessor which developed in England only started to be written down because of external influences.) Point is, all of the Nordic languages employ interjections akin to "Ah!", "Oh!", "Why?!", "Indeed!", "How?!", etc. So there really isn't any reason to think that such things wouldn't exist in OE as well.