If you feel tired after morning walk, it may be due to two reasons -
1)No proper sleep - If you do not feel fresh after getting up from bed and get tired soon after, that means to say your sleep is not proper. Please get up only after your full sleep and then go to walk, you will not feel tired.
2)Excess exercise - walking or any exercise should not tire you so much. One should do exercises only to half of his strength.
Next Steps
Make changes in your lifestyle. And if you are still tired, please consult a doctor.