No Appetite & Not Gaining Weight

I've always been a naturally petite person and don't gain weight easily. (I know I suck, people hate me for it but it's just the way my body is) The most I've ever weighed was maybe 117 lbs and it was due to a medication I was taking. Otherwise I usually sit around 105-110.

I'm small and it's a healthy enough weight for me but now that I'm pregnant I know I should be starting to gain weight. I'm 18 weeks and my morning sickness is gone but I just don't feel hungry. Of course I still make myself eat and drink a ton of water, but I just don't feel hungry most days.

I keep checking my weight on the scale hoping I'll go up even a couple pounds but it hasn't happened so far.

I see my midwife in 3 weeks and I know she'll say something if I haven't gained anything by then.

Does anyone who's struggled with this or knows someone who has have any advice? Is there a way to promote a healthier appetite or certain foods I can eat that will help with weight gain? Other than just junk food of course.

TIA