It is normal to see an increase of 8-16 lbs. (3.6 to 7.3 kg) within days of starting to eat to the minimum guidelines every day. It is equally common to see 20-40 lbs. (9-18 kg) within 1-2 weeks.
The increase is almost entirely attributable to water retention and it is necessary for cellular repair. Somewhere in the 4-6 week range the water retention starts to dissipate. That does not mean you lose weight (you are not looking to lose weight), it means that the water starts to be replaced by real weight restoration.
It takes 18 months to recover although you will not likely gain weight throughout that entire time period. From the time at which you begin weight restoration to the time at which your body weight stabilizes, the average per week weight gain is around 1-2 lbs (0.5 to 1 kg).
It is not a linear process and some weeks will be more and some less.
You stop gaining when you reach your body's optimal weight set point while eating the minimum guideline amounts. You should stop weighing yourself and focus on getting the energy in that you need instead because stepping on the scales usually precipitates a relapse.
You may also experience a lot of bloating after meals and, to you, your stomach or abdomen region will appear huge. Again, this lessens as the weeks progress and you get further along in recovery.