How much should I have lost within 8 weeks after sleeve gastrectomy?

I am 41 years old female. My height is 150 cm. I was about 100 kg when I had sleeve gastroctomy. I lost 9 kg by day 9 after surgery. Now after 8 weeks my weight became 86kg. Is it normal? I still eat few bites of small quantities. I dont eat sweets nor white sugar.However, what makes me worried os when I hear people say they lost between 20 and 25 kg within the first 2 months. Please I need to know. Note:I suffer from costipation.