Healthy weight gain?

My OB and GP both told me to gain 25-30lbs by the end of my pregnancy, but neither of them told me how much weight to gain when... ie, how much weight should be gained in each trimester.

I’m 15 weeks pregnant now, and I haven’t gained any weight. In fact, I lost a bit in early pregnancy (only about 4-5lbs) because of food aversions and also trying to eat healthier. I started at a healthy weight (not overweight, not underweight), but I’ve been holding steady at exactly 136.7lbs since I was 8 weeks.

Anyone have any opinions on if that’s okay, and/or what a healthy weight gain is timeline wise from here on out? I will talk to my OB about it again at my next appointment if I’m still concerned, but that’s not for another month.

Thanks!