Hatchling red eared slider health?

I have had theses kind of turtles for a long time but about 3 weeks ago, my friend got me a baby turtle while she was on vacation and it don't look likes it's in the best health.. It's shell is pretty soft (I think because it's not fully developed) the red markings on it's head are VERY light and not bright and dark like my others... and the inside of it's mouth is white not red? It eats a variety of food and basks normally but it is always sleeping as well.. Is it just because it's a hatchling and it's growing or is it sick?