Weight Gain

Suz
Hi! I am 22 weeks pregnant with identical boys. My acid reflux has been so bad (all along) that I have not been able to eat a lot or drink a ton. I have only gained less than 10 pounds. I've been a little worried it's not enough, especially since I've read weight gain is important up to 24 weeks. 
Any advice? Or how to eat to gain weight??