Congratulations Sonkie! - Women put on an average of 12-15kg in pregnancy this is due to the weight of the baby and placenta, the fluid around the baby, a greater blood volume to help the baby grow and extra fat stores for breastfeeding after the baby has been born. The majority of women will put weight on in the first two trimesters however this is not the case for all women. It will take 6-8months to lose the weight safely especially if you are breastfeeding. Its important not to worry about the weight you gain in pregnancy but to focus on eating healthily so your baby has the best start in life also breastfed baby's have less risk from developing childhood obesity
Hope this helps
Jo