It's normal to lose weight in the first tri especially if you can't keep anything down. I would still ask your ob about it tho!
Your body will take it tough before the baby does, but I second agrell, see your doctor.
I was the same way with my son...I lost a whole lot of weight first trimester and was put on meds so i could even keep anything down...and this one tried to do the same but i was put on meds right away which prevented that much weight lost...have you talked to your dr about putting you on some meds to help with the morning sickness