How much weight should I gain?

Samantha • My husband and I are proud parents of two beautiful children, our daughter is 5 and our son is 3 now we are expecting twins due October 11th!
Im 5'7 and weighed 110lbs before getting pregnant with the twins, now im 27.5 weeks pregnant and weigh 155 as of yesterday. My doctor says i am gaining well but i feel i have gained way to much in a short period of time. Any input would be great