Lost 4 pounds at 28 weeks

Mo
I’ll be 28 weeks tomorrow with twins and I went to my OB yesterday, apparently I’ve lost 4 pounds this month and my babies have gained 1 pound each. Which means I’ve only gained 20 pounds total. I have no idea how I’ve lost weight, this has been the laziest month of my pregnancy and I pretty much eat whatever I want. My nausea and vomiting finally went away this month so I know it’s not from that. Has this happened to anyone and why?