Trouble concentrating. Biting my fingernails when reading. What could it be?

I keep getting distracted. I don't know what exactly is going on. I don't know when it first came about, but I definitely noticed last semester (in college and I'm 26), my reading comprehension went down probably because I was biting my fingernails while I was reading. Sometimes when I'm talking, I'll forget how I was going to end things. A lot of times when I'm talking, I will go off into tangents that are so far off from the start of what i was going to say that my conversation is in a totally different place. I ramble and jump from topic to topic, people say. What are all the possibilities here?