1. There is something called physiological insulin resistance (PIR), which is not the same as the insulin resistance we, as diabetics, may have. It does happen to some people after very low carbing for a period of time, but it is also fairly temporary. If this is what your problem is, just carry on as normal and forget about your FBG. As long as your post meal rise (from before to after) is not increasing, there is nothing to be concerned about. It happened to me earlier this year. My base level increased by above half a mmol/l but the rise after a meal actually improved. This meant I may have been slightly higher, but I was flatter with much less variance, and this is what is important. My PIR disappeared after a couple of months and now my base levels are what they used to be and my post meal rises have stayed at the improved level. Win, win.
2. You need to make plans about a maintenance diet well before you reach your goal weight. I didn't, and I just kept on losing. You can up the carbs, but that isn't wise. You can up the protein a bit, and you can up the fats. It took me 2 months to steady my weight, which is why I said you need to plan in advance. It wasn't easy. It is a fine balance and may take a bit of trial and error, so your scales will become your second best friend after your meter. I upped the fats, but as this involved introducing (amongst other things) cheese and more eggs to my diet, it also involved extra protein. I did not up the carbs. I eventually found the right balance and have now maintained my goal weight for over 18 months.