NSFW Why has my chest size gotten dramatically smaller ?

I have always had a size 36D breast size since I was 16. I’m 21 right now, but for the past month I’ve noticed my boobs have gotten smaller. Now they’re at 32 inches compared to when they were 36. I don’t know if it’s because of weight loss, but I haven’t lost any weight recently. I’ve even tried taken birth control pills but my body hasn’t changed. I think they’re a size 32C now. I don’t know why they got small out of nowhere.Has any other females had this experience ? I get my periods on a regular and don’t do any drugs.