I'm 32 weeks tomorrow and I'm still down 4 pounds. I bottomed out on my weight loss at 15 pounds. I think I finally started to gain weight back around 19 weeks very slowly and it recently picked up at about 28 or so weeks. My doctor wasn't concerned however because I started a little over weight. If it is something your doctor is concerned about they will let you know. Typically most of the weight gain is in the 33rd trimester when your baby starts to gain fat.
with my pregnancy, i didnt gain any weight until about 5 1/2 months. my dr was actually concerned because i had lost weight instead of gaining, due to my morning sickness. but by about 8 months i gained the weight that i should have and by the time i went into have my son (i was induced at 41 weeks) i had gained all the weight i possibly could and delivered a healthy 6lb 14oz baby boy.
With my first pregnancy I lost weight for like the first 3 months then slowly gained weight after that :) and now with my current pregnancy I've also lost weight and I'm currently 5 months pregnant
My trick is to eat a bagel with a carnation instant breakfast. Can't drink it alone though or I vomit