If this Nether was first generated, there should be a fortress somewhere very nearby. Every fortress I discovered is at least up to ten chunks away from the portal. Just bring lots of cobblestone, 'cause you're probably going to have to build indestructible bridges from Ghasts.
If you have your distance rendering set to short or tiny, consider putting it on normal or far for a sec just to look around. I did this at my Portal, and while I couldn't normally see a Fortress on my usual sight distance (Short) I was easily able to spot one when I turned it up, which allowed me to make my way over to it.