You may not be suitable to wear the contact lenses because of the maladjustment. Your pupils may shrink when you wear the contact lenses. You need to pay attention to this. If you want to wear the contact lenses to help you see clearly at the things, you are suggested to wear the eyeglasses which should be better. You should take this one into consideration.
It sounds weird cause there is no evidence to show that contacts can cause sleepy. And there are many others reasons to render you sleepy, such as weather, eye strain, lack of rest and so on. But if this just happen when you wear the contacts, I think you may go to the optical shop and check whether the prescription of the contacts is suitable for you. If it dose not work, you had better choose another one to have a try, and if the symptom still exist, it means you are not suitable to wear contacts in reality and you have to consult an eye specialist for help in consideration of your eyes.