Something I've always considered that I feel most people don't think about, but, the heavier you are, as long as you maintain the same physical activity level, the more calories you'll burn. This is simple physics, but it obviously takes more energy for someone that weighs 175 kg to take a step than for a 125 kg person. Thus, if you're eating 3,000 calories/day now and you're gaining weight, as long as you 100% maintain your activity and calorie intake levels, eventually, you'll plateau and no longer gain weight. Where that plateau lies varies from person to person based on what they're eating and their level of activity, but it definitely exists.
Personally, I think gaining 4-5 kg in one week is a bit on the high side, BUT, as I said, you will plateau eventually. Worst case, you feel like you are a bit too large, you can cut back the calories a bit and slowly shed off a few kgs.