I have heard that side effect with some people.
Honestly, 100 mg is a really low dose so I am surprised it is making you feel tired. Perhaps it's too much for you?? If you are so tired that it could interfere with your driving then I would definitely tell your doctor. What time do you take it? Perhaps if you switch it around and take it a few hours before bedtime, that would help.
I wouldn't, of course, do anything without talking to your doctor.