Good but also not good
I eat and don't gain weight but I'm constantly hungry, I can eat meals fit for 2 or more people sometimes and would still be hungry. I went on a school trip once and the teacher told me I was cut off from buying and eating more food... this situation has happened more than once. There are also many moments of hunger pain when I don't eat enough and it hurts real bad.
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Maybe you have worms in you. Most of the symptoms you have point to that.
If it's permanent, I would suggest you go see a doctor. '^'
If it's only a few days/week in a row and then it stops before starting again a few weeks later, I would say it's puberty and it's not alarming. Unless you've finished growing up that is. (Around 20 for women and around 25 for men.)
If you're loosing a lot of weight in a short time (like 10 pounds or more in 4/5 months or less), you have to go to the doctor, because it could be serious.