Water Retention?

Je
So I'm 38+4 weeks today and I've only gained 16 pounds this pregnancy... Until this week! I gained 3 pounds and my doctor was a little concerned! I didn't change my eating habits (except a little Halloween candy 😁) and I am more swollen than before... Is this normal and is it just water retention? I'm nervous to keep gaining weight like that when I've not been eating more than normal.