There is a bubblelike thing on my gums. It is pink and swollen. What is it?

Most likely a canker sore; almost everyone gets them at some point. They're caused by stuff such as brushing your teeth too roughly, lack of flossing, and even stress. Your toothpaste too, however, may also be causing it or aggravating it--if the paste contains sodium lauryl sulfate, switch to a different kind (preferably natural) while you have the sore. I recommend rinsing your mouth with saltwater or baking soda mixed into water, as well as avoiding spicy and acidic foods at the time, because they can make the sore worse. Eating yogurt might help as well.
Good luck with the sore, I know they're a pain!