So confusing

So I got this positive about a week ago, and ever since I’ve gotten negative. I’m not sure if it’s because I’ve been dehydrated ever since or what’s going on!! I hope someone can help!! I’m on cycle day 48 and my cycles last 38-40 days. My mom ovulates late, so I thought maybe that’s why I haven’t gotten another positive. But I’m not sure why I got one in the first place. I looked it up and it says being dehydrated can cause a dip in hCG levels. Wondering if it’s happened to anyone else. I’d appreciate it! Thanks!