For most people with a herniated disk, low back pain is the initial symptom. This pain may last for a few days, then improve. It is often followed by the eventual onset of leg pain, numbness, or weakness. This leg pain typically extends below the knee, and often into the foot and ankle.
Iron Nuggets are used for crafting very basic thaumaturgic tools, including your very first wand. Besides crafting, they can be produced as bonus material by the Infernal Furnace.
Just keep mining. You will eventually find iron ore which you can mine with your stone pickaxe. It may take a while, but the deeper you go the higher the chance of finding iron. It's there, you just have to find it. Once you do, build a furnace and put your iron in the top and coal in the bottom and your iron will smelt into ingots, which you can use to make all sorts of nifty things.