2nd trimester hunger

I'm 21 weeks and I can't seem to feel satisfied after eating. I liberally just finished dinner and all I can think about is eating a bowl if cereal. I know your supposed to only be eating an additional 300 calories but I think I'm surpassing that number daily. I just feel hungry all the time! Anyone else feeling like this? Do I need to put these cravings in check? I have only gained 6 pounds since my pregnancy began.