Confused about weight gain

hiya!

so, as I just hit 30 and realised that I was at a stage where I was gaining moobs, I decided enough was enough.

I barely eat chocolate or cakes anymore, cut the drinking down to 10 units a week from 50+ (alcohol dependant) and started what i thought was a better diet.



I work 12 hour shifts five nights a week with light to medium lifting throughout.

So I calculated I would need 2700 calories a day to stay the same weight (I'm male btw) and decided on a rough diet listed below.



a day roughly on average



200-300g of plain chicken

100-150g fish (or the delicious tuna light lunch)

1-2 bananas

1-2 small oranges

bowl of cereal with semi skimmed milk



I do drink diet cola and an energy drink a night too.



Considering before I would eat micro meals, store bought sandwiches and cakes, I am shocked to find on my new eating habits I am still gaining weight.



am i missing something very obvious?



thanks all