I am so hungry and weak

I have gained alot of weight this pregnancy but I also keep an eye on what I eat mostly through the weekdays. I eat about 2000 calories a day like I should but some days I may not meet that and I feel fine. Today is the second time where I just feel like I'm going to pass out from low blood sugar. I ate breakfast and about an hour later I felt like I have ate nothing and got so weak so I ate a banana and a little bit of sugar to help and nothing. So I decided to make lunch. I just finished about a half hour ago and I'm starting to feel like I haven't had enough again I dont understand? I dont wanna just eat everything all day and continue to gain weight and risk gestational diabetes. What should I do?