You can get it on the tongue, but there are many things that can make your tongue sore. Even just biting your tongue, eating something real crusty, or drinking something too hot. If it's a canker sore (from trauma) it should go away in a day or so, unless you keep biting it, etc. If it takes over a week and seems to get worse, it may be herpes or another kind of infection, like a bacterial infection. Rinse your mouth with water (and drink water) a lot.