The interesting thing about stress is, you can often be more stressed by deciding that you have nothing to acftually be stressed about!
Even though there is no bvious cause in your life, you do exhibit signs of stress, which need to be addressed.
It may simply be delayed reaction to your exams, or issues with your personal relationships, but what ever the cause, this needs to be sorted.
First of all, get yourself a healthy diet. Cut out junk food, cut down, or out, sugar, spicy food and alcohol. Try not to eat at all after seven p.m.
Get some exercise - walking or swimming regularly, but don;t go mad, just a walk fast enough to get you breathing deeply for about twenty minutes a day will help.
At bedtime, ensure you are relaxed for at least an hour before you go to bed. Have a warm bath and a hot drink, and when you go to bed, make sure your room is well ventilated, and you have a nice lightweight duvet or sheets.
Try and read for half an hour before you go to sleep - don't watch tv or films.
All these strategies are proven to help with stress, and you should see some benefit farily quickly.
Good luck.