I thought he was just tired from thrashing around so much while Annie dodged them all. She herself was tired because she transformed before already and had to also regenerate from the cuts before.

As for her form, she's got good proportions. She's not centrally obese, doesn't have lanky limbs and doesn't have a stupid smile on ehr face. In fact, none of the the human titans smile like the non-human ones. Eren's "grin" (even though it's just the way his mouth curves upwards) is as close as they get.

It also just occured to me that the other three human titans lack skin (armour titan has his armour.. but it's not skin underneath, right?), while Eren's the only one who doesn't show off his muscles.