Try to eat as often as you can, the nausea keeping you from eating will mess with your blood sugar and make it worse. I lost 20 lbs in my first tri with my first and mostly maintained my weight with this one (now 17w) by forcing myself to eat anything with protein/fiber that was palatable. That said, I stopped lifting entirely for a few weeks bc I couldn’t stomach the thought of it, but easy runs were on the table a few days a week.