1st trimester weight gain

I started off pre-pregnancy around 167 lbs (5'9" with a BMI of ~24 so not overweight to start with). I haven't gained any weight in my first trimester and am just about to hit week 13 on Tuesday - I've actually dropped a couple lbs since my initial weigh in. My doctor says everything seems fine; baby's heart rate is strong and healthy and I haven't had any issues with morning sickness or difficulty eating so it's not like I've been eating any less or had trouble keeping meals down. This is my first pregnancy so I'm definitely anxious about everything going well, but is no weight gain normal/fine in the first trimester?