gaining too much weight

Okay ladies so I'm 6 weeks pregnant I found out I was pregnant New Year's eve before I knew I noticed I had gained 5 lbs during Christmas and I wasn't doing anything out of my normal routine and that was my first sign something was up I was 165 pre baby and now I'm 172 😖 im trying to cut back on eating out And all that I only drink water so I don't get why I'm gaining so much but tbh I felt like I've been eating the same before I was pregnant and I used to drink a lot and never gained weight I don't get it