100g is fine. At least your weight is headed in the right direction! I know how depressing it is to be losing weight so slowly when you modify your lifestyle so much, but if you'd been losing 'only' 100g per week for the last couple of years you'd be at your goal weight by now. So even if it takes you two years to get there at least you'll be getting there! It may be some small comfort to know that statistically the slower you lose the weight the more likely you are to keep it off. Hang in there. It could be worse, I've been on a plateau with no weight loss for the last month. And given I gained weight over Christmas and New Year that's not good!
Anyway, the fact you didn't lose more could be caused by many things. You could be retaining water from the heat, from not drinking enough water, or even from eating salty foods. Also, have you checked the portion sizes and calorie counts of the healthy foods you are eating? For years I couldn't understand why I was gaining weight with a vegan diet. It turned out to be portion sizes, lack of exercise and choosing the wrong 'healthy' foods (I loved curries made with coconut milk. When I found out how much fat and how many calories it contained I nearly died!)
Above all, don't stress. This whole weight loss thing seems to be a bit of trial and error for most of us. If there were one trick that worked for everyone there wouldn't be so many diet plans out there! Chances are you'll find what the problem is and bounce back next week!