I'm sixteen and was just diagnosed add, should I take ritalin (methylphenidate)?

Maybe. First - work with your doc to make sure you have adhd. One requirement for diagnosis is having symptoms since before age 7. Adhd shouldnt just pop up out of nowhere at this age. Then, proceed with discussing treatment options with your doc. Ritalin (methylphenidate) is a very short acting medication and for teens, may need to be taken 2-3 times per day. There are other long acting options that may fit better.
No. It is better to find the cause of your symptoms than just cover symptoms with drugs. Allergies, nutritional deficiencies, low blood sugar and learning problems could be the cause. These can be treated without drugs and without the side effects that drugs can cause.