Please call and talk with your doctor or to schedule an appointment to ask directly why this medication was prescribed for you. That should be explained thoroughly at the time so you understand when and how to take it, and what to expect.
Never leave your doctor's office without a clear understanding of the treatment and medication. Take a notebook with you to write down what your doctor says, as it can be hard to remember later, but it's so important.

Also let your prescriber know if it isn't something you want to take. It's very important that your doctor knows how a medication is affecting you. There may be something else available that doesn't have the same side effects.