Help with Calorie Intake

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Hi. I'm currently on day 11 of insanity - I'll be starting day 12 in a bit; second insanity workout of the day - but I'm getting confused with the calorie intake. In order for me to get these workouts in and completed on schedule I have to work around other people schedule - people who I live with, so I tend to double up on days I know I won't be able to do. Anyway, before starting insanity I was eating around 1700 so I left my calorie intake at that and then ate back any calories which I burned - I eat around 2100-2600 somedays and I'm now starting to wonder if I'm eating too much! This morning I worked out my calorie intake by using the insanity nutrition guide and it worked out that I should be eating 1800 calories in order to fuel my workouts and still lose weight. Now does that mean 1800 calories and that's the limit, no more food,etc, or do I eat back enough calories to net 1800? I'm also still hungry when I eat 2600, so anything less may now be a struggle, I also hink that could be down to the fact that before starting insanity I was eating low carb, high fat - I did this purely because I was always hungry when I ate higher carbs. I know I'm only on week 2 but I have gained about 3-5lbs and also inches here and there, which has me wondering maybe it's water weight because my body is being put under stress with these workouts and it could also be down to the fact that my body is adapting to higher carb and holding onto water weight. Which ever it is, I just need help with the amount I should be eating because at the moment I feel great energy ways, but fat and bloated physically, I also want to get my intake right because I don't want to end up burning out, which has happened on an easier program.

Thanks ????