Hello. I'm Currently Going Into Middle School. This Past Week,

Hello. I'm currently going into middle school. This past week, I've been experiencing some weird symptoms that I can't really explain. I consume more food than I normally would (I'm not a very glutton person, as I am almost 20 pounds underweight), I feel rather moody at certain points, and I get random pains in my lower stomach. I'm not completely convinced it's my period. But, I'm still a little concerned. Help?!