4 weeks and losing weight???!!!

Hi girls. I just found out that I'm 4 1/2 weeks pregnant and I've lost 6llbs in 4 days? Has anyone else experienced this? I was overweight and on weightwatchers before finding out the great news so this is a bonus. Have cancelled WW as apparently it's not safe to diet whilst pregnant but have been eating constantly and healthly and have lost weight without even trying? Is this safe? My first docs appt isn't until next week so just wanted some thoughts to put my mind at ease in the meantime! X