What Causes Pain In My Stomach?

i'm from pakistan doing MBA,my age is 22, i have a problem in my stomach before 7 mounth and still now,
The problem is when i'm hungry i have a pain in my stomach.
And also burning in stomach even not hungry or eat something,
And my weight day by day decrease ,i,m so worried,
Now my friend and my colleague avoid me and me also decrease my confidence.
Now i start NEXIUM CAPSULE 40 MG before 3 week and now feel i'm much better then before but doctor tell me eat this continuously 8 week,
so please suggest me what i do, can i eat this capsule 8 week,
i'm very thank full to you,