I’m loosing weight and I don’t know why

So I am 15 years old and 5’4 and around January-March I really struggled with my body and I was under eating a lot (during this time I was 97 pounds) so from March to April I really worked on transitioning back into eating like a normal 15 year old. I’d say around May I had achieved normal eating habits and my body was responding really well to them (During this time I was 94 pounds which was around the weight I was before I was under eating.) now it’s Near the end of July and I eat like a normal person, I eat every meal and I eat 1-3 snacks a day, I really don’t stress about what I eat at all anymore (I stopped counting calories) and I eat dessert if there is a dessert, so basically I eat like a normal 15 year old. Recently I went to a water park near my house and one of the slide patrol people asked me to step on the scale, and the scale read 89 pounds, and I didn’t believe that at first so I weighed myself at home and it’s true I’m 89 pounds now. I don’t know why though because I have not made any attempts to loose weight (I literally ate a cinnamon bun for breakfast.) so now I’m super worried and I’m wondering if any of you know why I lost so much weight from doing nothing. Update: I went to my doctor and weighed 88 pounds and she told me that I should be heavier especially for my height, but she said I’m healthy. but a couple months later (September) I weighed myself and I weighed a horrifying 83 pounds :( (you can probably imagine how gross I looked.) family members were getting worried and so was my dance studio and me! I went to see a nutritionist and I’ve been working with her for over a month now. Currently I fluctuate between 84 and 85 pounds! Hoping to gain more and look healthy :)