When you say you are tiring after a workout, there could be a couple of reasons:
You must find time to cool the body down by stretching out each muscle group so as to bring the body back to equilibrium. This way the lactic acid build up gets dissipated and does not catch up with you.
Also, you should try and eat a fruit like an apple or banana or any carbohydrate-rich food like a cereal so that it does not deplete you of your energy. Eat it at least 1/2 hour before your workout, if it is a light fruit or an hour before if it is any cereal. Including some relaxation techniques into your workout may help you deal with the tiredness.