the reason why you gained weight this week is that you body put on some good muscle which is great for burning fat.

BMI IMO is not a good guide to whether you need to lose weight or not it does not take into account what build you are whether that be small medium or large build and that is important to take into account for wanting to be sure that you are in your healthy weight range.

it sounds like to me that you are on the right track and I would keep doing what you are doing thou i would back off just a tiny bit on the exercise.

do NOT give up keep going it will be worth it we all have those frustrating weeks where the weight does not move or it even increases you will find that next week you should have a loss again and maby a big loss.