Trouble gaining weight

I'm 16 weeks and 4 days and at my last appointment last week I lost more weight making that a total of 8 pounds since I got pregnant. I've never had morning sickness and I feel like I'm eating a lot all the time but I can't seem to gain weight. Any one else have this issue or know any good tips on how to gain weight? Like I'm literary eating pizza and McDonald's (I know it's not good for me). I eat a lot. 😡