Need some help!

I am ALWAYS hungry! Even after I eat in 20 minutes I'm hungry again! I know you're only supposed to consume an extra 200-300 extra calories a day according to my midwife but I feel like I'm failing at that due to the fact that I am hungry all of the time therefore always snacking. I don't want to just be hungry because I feel like I'm depriving my baby of nutrients they may need. But I'm tired of always eating and I'm afraid of gaining to much weight... How can I stop this constant hunger?