2 months... 13kg lost.... too quickly??

If you have a lot of weight to lose, it can come off more quickly in the beginning. When you first start your new lifestyle, a lot of the weight loss may be water weight and the weight loss will slow down and you continue.

After the first month, you should be losing 2 pounds per week or up to 1% of your body weight per week, whichever is higher. If you are losing more weight than that after the first month or so, you may want to increase your caloric intake.

There is no specific coloration between the speed of weight loss and gaining it back. What matters is that you make life changes that you can sustain for the rest of your life.

I am still losing weight at a good rate, and by good rate I say between 1-1.5kg a week.
I usually burn approx 1000 calories in a gym session, but last night, managed 1.5 hours and smashed out 1500 calories...

The best thing is that I havent pulled up sore the next morning, so I can do another good session (probably 1000 calories) tonight.

With all due respect, I don't know of a sport where in a gym you can burn 1500 calories in 1.5 hours. You might want to check your numbers again, so you don't get used to logging too much burned, because it influences how much you eat and that in return affects how much you lose. I have never heard of anyone burning 1000 calories in one hour......unless you weigh at least 260 pounds and do an hour of jumping rope or spinning without stopping......then 1000 calories an hour are possible, but unfortunately most people who weight this much are not able to skip rope or spin for an hour.