What changes are there when being treated for hypothyroidism?

Varies. Symptoms for hypothyroidism are diverse and nonspecific. Some of them might not be caused by hypothyroidism although they fall in the relm of hypothyroid symptoms. Best thing to do is to get the hypothyroidism treated and see which hypothyroid symptoms disappeared or improved.
More energy? You should feel slightly more energy, not be as cold, and constipation may improve.
Many. If your hypothyroidism was significant and for a long time, you should expect improvement in attention and focusing, improved energy level, regularity in your menstrual cycles and less edema/water retention, especially around the eyes and legs.