Forearm pain: The top of my right forearm hurts... can you give me a diagnosis?

So the other day I was cliff jumping with some friends and dove off a cliff that was about 30ft. From what I remember I think right before I hit the surface I looked up and when I hit the water it felt like i hyperextended my right hand and felt like the back of my head almost touched my back. Now my lower neck and shoulders are pretty sore, and the top part of my right forearm is really sensitive to pain, especially when my arm is parallel to the ground and I lift my hand upward at like 45 degrees (if that makes sense)....

Do you have any idea what is causing so much pain in my arm? I was guessing maybe i slightly tore a muscle? Also, can you give me an estimation on recovery? Thanks. Best Answer ASAP