Hi Alicia,
I think something wrong has happened to him in his short life. Get him to therapy asap and see what the professionals think. Maybe something has happened you are not aware of? But he needs help and quickly.
Dear Alicia,
I know how frightening this can be because I have been there. What I ended up learning was far more terrible than his behavior. Remember that children are very good at modeling what they learn. The way I see it, there are two possible sources 1) being exposed to violent, profanity filled TV, video games, etc. 2) being exposed to violent, profanity filled behavior from someone in his life and you really can't rule out anyone right now.
In my own case, my ex-husband would abuse and swear at my children if I ever left them alone with him. They were threatened into silence. This is why he is now my ex. One of my first clues was my then 6 year old son "entertained" other children by saying "motherf***ker" over and over. This is a word I NEVER used. Much later I learned that my mother-in-law hit him. There are a lot of secrets in that family.
I urge you to take a careful look at anything and anyone your son is exposed to. If it is videos or TV, you can make sure he sees age appropriate material. Make certain no one else shows it to him. If someone (teacher, coach, husband, step father, uncle, etc.) is hurting him and/or violent then your job is much harder because you have to protect him. Abuse is a minimized epidemic and I hate to be the bearer of bad news, but for the sake of your child, you can't turn a blind eye. My ex carries knives and guns. I later learned that he made threats at gun point.
Talk to your son. He may not tell you much now but give you "bread crumb" clues. Good luck and God Bless!
Anna