23 week weight gain help!

Alannah
I've only gained 6 lbs. My midwife said she needs to see more weight on me by my next appointment but I just don't know how to gain more. I give into cravings (bread, milk, meats) I eat veggies but not nearly as much as I did before pregnancy and I have a Coke a day (baby loves it) and not something I did before pregnancy either. I indulge when I want and trust me when my little boy is hungry he lets me know and I feed him lol which is every 3 hours or so. I do walk a lot because of my job and I have not set foot in a gym since 18 weeks because of sciatic issues, so I am not burning unnecessary calories. I just don't know what else I can do to gain weight. Any suggestions? Any ladies having the same issue?