There are many different disease processes that can cause your tongue to be sore. The most worrisome and the one that every physician wants to make sure that you don't have is cancer. Squamous cell cancer (SCCa) is the most common cancer in the head and neck. It is also the most common tongue cancer. The two most common causes of SCCa are smoking and drinking, so when you go to a physicians office to get checked out (which is what I am recommending), they will likely ask you about both. Recently there has been a significant amount of research that is showing that there are viruses called the Human Papilloma Virus (HPV) that pre-dispose patients to oropharyngeal cancer. Now all of this information about cancer isn't supposed to scare you, but rather to help you understand why ruling this out is the top priority of whatever physician you go to. There are of course many other disease processes that can cause oral ulcers which are non-malignant (i.e. not cancers), and are much more common than cancers. For instance the herpes virus (HSV-1) is the typical culprit in what people refer to as "canker sores" and can cause painful ulcers in other locations in the mouth. Some bacteria can do the same. Also autoimmune processes (where the bodies immune system is attacking itself) can also cause ulcers. I would definitely recommend making an appointment with an otolaryngologist
(ENT) to get evaluated if this painful spot has been there for more than a week or two. Best of luck.