Rash on thigh

La

My daughter just started getting these rashes on her thighs. Is this just a diaper rash?

They come so suddenly and look so painful. She has never even really had much of a diaper rash on her bum even. I’m almost wondering if maybe she is allergic to the diaper or if maybe you guys think the diaper might be too small? It doesn’t look to small...but could that be causing it?