gestational Diabetes

I was just told I have gestational diabetes. I’m so upset about it. It’s my first baby. I’m a small, only 125 before pregnant. I am starting my third trimester this week and only gained about 5/6 pounds. I am pretty healthy and everything with me and my baby have been going well. This pregnancy hasn’t been bad at all until I found this out. How does this happen? What should I except? Will I be able to eat pasta still? Lol how strict is the diet? What happens if I do happen to have too much sugar? Thank you for any help/advice!