Signs of diabetes?

I am currently 25 weeks and my baby is already measuring at almost 4 pounds!! My stomach is measuring 2 months bigger than it's supposed to be, and Ive gained 38 pounds since being pregnant. People say I may have diabetes, and it's scaring me really bad!! Please let me know if these are signs!! And also please let me know the main signs of diabetes while being pregnant so I can tell if I have any of them. Thank you in advance!!