Losing weight/lack of appetite

I am 13 weeks 3 days and for about 7 weeks I've had a much smaller appetite and have lost 10 lbs. My nausea is coming back with a vengeance. My doc said if I have gained at the next appt I'll be ok. I am worried though bc I know I'm not eating healthily enough when I do manage to eat. Was anyone like this at the beginning and had a healthy pregnancy? My baby was ok at 12 weeks 3 days but I do know the head measured 1 week ahead. They didn't say anything but I saw it bc I videoed the ultrasound. I'm very worried and need some encouragement!