What Causes Fatigue And Lightheadedness During Menstruation Post Surgery?

hi, im 32 years old and I had an laproscopic appendectomy 2-3 weeks ago. Recovery was fine until this last week as my Period also came. I observed that when I stand for long periods of time, I would feel tired. and then the last 2 days I have been feeling weak, fatigue and light headed. Is this normal or could this feeling be because I just had my period?