Girls, help ? My kid has been afraid to bathe for the last week. He us…

Girls, help ? My kid has been afraid to bathe for the last week. He used to love it so much, but now he's freaking out. We bathed him in a tub with different water levels, but the temperature is always fine, but one day he screamed and cried. I thought maybe something stuck on his bottom (like diaper rash). I looked and everything was fine, but just in case, I put some Sudocrem on it. He still cries when we try to bathe him. Then we went to the shower together - he also cried! But when I wash his underarms, everything is ok. How do you fully bathe him? What the heck... I don't even know what to do anymore.