Yes I think everybody lose weight in the beginning.
Many people do in the beginning, however my mom whom is smaller than you has had 5 children and she always had trouble keeping weight on in the third trimester and they would try to get her to put weight on. Now me, I am normally around 165, but before I got pregnant this time with my second baby was 218. I dropped down to 204, jumped back up to 210 for the majority of my 2nd trimester and now am 36 weeks and 4 days and am at 213 and my doctor is fine with it. Just eat healthy and get enough exercise and you should be fine, talk to your doctor about it, they'll know if there is reason for concern, every pregnancy is different!
Don't stress hun. I always loose weight when pregnant! ;-) the doctors always have a little freak out. But I'm short, so once the baby reaches a certain size I can't eat enough to put anything on! Otherwise I feel sick and bloated and just terrible. By the time I reach 38 weeks, I am usually 10kgs lighter. Once the baby is born at least 15-20! My babies grow fine too. Better than. High apgar scores and they're larger than normal...between 8-10 lbs!