Acid poop ahhh

So my toddler is 22 months old I don’t change her diet she is pooping so much sometimes that it burns her idk if it is quite acidy or just that she poops so much that it burns. I wash it in the sink with soap and water every time! And put the best cream on her triple paste butt cream. And put her pamper diaper on. I air dry it often as well. I don’t no what to do. It is very uncomfortable for her she screams sometimes when I change her this been going on and off for 4 weeks. Should I bring her to doctor ?