Hello....I'm 41 Years Old, I'm In Really Good Shape, I

Hello....I'm 41 years old, I'm in really good shape, I workout 3 to 4 days a week (strength training and cardio). I had blood work done to see if I'm going through pre-menopause. Blood work came back negative. However; my menstrual isn't consistent and I have hot flashes and night sweats (wakes me from my sleep). What could be the reason for this? I really think the results weren't correct