Any advice for getting enough fuel in for a smaller person newer to running long distances???

I’m currently training for a half marathon and I just have some questions regarding nutrition. For some context I’m on the smaller side, I’m a woman and about 5’5 and 105lbs. I’m also running between 35-40km a week as of right now. My long runs are like 15km. I also run between a 6:05-6:20/km time. Up until I started doing the long runs, I found my energy was completely fine and I felt pretty good, but when I introduced the long runs about a month ago I have felt more drained than usual. Likewise, my body has been slow to bounce back after runs and my shins have been painful.

I think I likely need to eat more carbs but I’m finding fuelling difficult. I’m definitely trying to eat more, but I’m a super picky eater and I just don’t know when/how to fuel for this amount of km per week (I know to many it doesn’t seem like a lot but to my body is certainly feels like a lot!!). Also for a little extra context I am a vegetarian but I eat lots of dairy!

If anyone has any tips or recommendations that would be greatly appreciated!! Particularly any snack recommendations would be awesome lol!!! I’m looking forward to running the half and want to give it my all!