Help? I have a question about my stomach retaining water.?

So I'm 15 and my body has all of a sudden started to retain water. Every morning I wake up my stomach is normal and flat like it usually is but as soon as i drink some water it starts to blow up like a balloon and it's like that throughout the rest of the day and it starts all over again the next day. I also haven't had my period in about 5 months. Could that be part of the reason of why this is happening? Could midol help me get rid of the bloating that i get from water retention? Are there any quick remedies for this? Please help me.