You could have worms, or even have herpes. These can be serious, also can make you underweight since they eat your food. Judging by your weight I can see that you may infact have worms. Go to the doctor, quick.
You may also have piles, if you have pick them out with your fingers.
http://www.youtube.com/watch?v=bvIlVC87-uY
hepatites b
:D:DD
You may also have piles, if you have pick them out with your fingers.