There is no evidence to show that sunglasses can cause sleepy, you know there many reasons make you sleepy, probably you just tired. You said that when you wear sunglasses, you feel sleepy. So may be you are tired and the dark light makes you less energetic. Maybe you think about whether these days you are lack of rest or sleep. You can have your eyes a rest after one hour's work. Just look out, your eyes will appreciate you very much!
But if this just happen when you wear the new glasses, I think you may go to the shop and check whether the prescription of the glasses is too strong.
Something can cause eye fatigue, such as weather, eye strain etc. so don't play computer games or watch TV for too long.
It sounds like you have some difficulty wearing your sunglasses. Anyway, from what I know, there are some types of sunglasses that are not suitable for anyone of us. See what I mean, you have to choose the right type of sunglasses and you'd better consult a doctor or optical professional for help. So you should go to the optical shop for some advice and try not to wear them for much too long.
Did you get enough sleep last night? Are you tired? If you are tired or you didn't get enough sleep, you can be sleepy. Maybe it is because the light is too dark when you wear your sunglasses, dark light can make people sleepy, too. In order to change the situation, you can try another pair of sunglasses or buy a better one.