Girls, hello ?? The child has had a fever since Friday and it fluctua…

Girls, hello ?? The child has had a fever since Friday and it fluctuates sharply within an hour, possibly 5-7 times going up and down drastically. Yesterday we saw a doctor, she said to wait a couple more days as she didn't see anything (what I found strange). And from evening 40.5 and it goes off very hard. Has anyone experienced something similar? I would like to ask for some tests to be done, maybe someone knows what kind?