Growing pains. I am 17 and I get these fairly often. Unless it's hurting terribly, it's not something to worry about.
physical activity too shortly after eating
If the pain is in the lower abdominal area on the right side, it could indicate appendicitis. It could also indicate an ovarian cyst (pain on either side - not just the right). If you have fever, or...
Repost and tell us the 'right side' of what. Head, knee, eye, foot, etc.
I don't know but you should take a salt tablet
Many things such as: 1) Costochondritis 2) Torn/pulled muscle between the ribs 3) Heart Attack 4) Pulmonary embolism 5) Broken Rib