Hello
Since you are 18 years old and having pain in abdomen ( but you didn't mention the site , where there is pain , so it is very difficult to say the reason of such pain), , this type of pain may be due to these reasons , these includes.
1 Hyper acidity or
gastritis , usually such type of pain may be due to hyper acidity caused by greasy , oily , spicy foods , drinks with caffeine in them also causes such pain. Pizza ,burger should be avoided. It also might help to avoid drinking or eating for 2 hours before you lie down. Take some
antacid but if symptoms are sever you may need drugs like pantaloc- d once or twice in day.
2 the next reason in such cases may be due to tension or
anxiety , so please avoid such type of things.
3 Overeating or no rest after eating is another cause of such pain.
In my opinion deal as mentioned above.