I've found that snacking is best. I eat smaller meals but eat snacks constantly. You can always go for healthy snacks or even salads. I also eat a lot of pastas which aren't that great health wise but it does keep me fuller longer. I'm not a big fan of meat so a lot of my snacks have something with peanut butter (which also helps stay fuller longer without eating a massive amount) If i get too hungry after just eating, a glass of milk works well too. I can't stomach water but if you can try that too.
One thing i have noticed with pregnancy is no matter what you do you could still gain a bunch or barely at all. With my first son I had extreme morning sickness the whole time but still managed to gain 100lbs with him. I'm working on my second son now almost 23 weeks and I lost a lot of weight up until a few weeks ago and so far have only put back on a pound and a half. If you are really trying to avoid the weight gain staying active is the best way to do so (only if your doctor allows you to be active).. hope this helps.
The whole key is to eat healthy. It is normal to go through phases where you are more hungry than other times. I have to eat every 2-3 hours or I am starving and get sick. Just eat snack high in protien and good for you such as fruits and veggies. Carbs are the worst cause they don't last long and just turn to sugar. Eggs, Peanut Butter, Nuts, etc are good ones too.