Have you got other goats or sheep in kid / lamb?
I've got one goat that every year gets picky, goes off her feed and gets thin every year around this time.The first year she was extremely thin and I took her to the vets, all sorts of tests and £100 bill concluded she was a very healthy bag of bones.
As soon as kidding starts she starts eating again and steadily gains weight till next year.She's not kidded herself for 5 years but had a cloud burst pregnancy after I finally dried her off and retired her last autumn. She's just very tuned in to all the pheromones whiffling around.