Diarrhea

Kkk c

My almost 18 months son has been having diarrhea and stuffy nose. Some poop is liquids some are not. Also, his poop has very foul and sour smell and the color is like very pale yellow. I called up the doctor and she said there’s not much we could do about it so kinda let it passed and it can last up to 2-3 weeks on some case she sees. This cant be right, right? Last night he couldn’t really sleep because he pooped 3 times and he was just very exhausted I can see. His appetite also decrease and is already losing weight because of this. He already not doing well with weight gain and now seeing how he’s not eating and constantly poo and uncomfortable, i feel really bad. Does anyone child go through something like this?