Help me to maintain my weight

Hi,

I don't know if it's because of my job (technical support engineer) which requires to be quite flexible, but I find it quite hard to maintain weight. Some day I will lose a lot weight (especially after a workout session), other I am going to gain a lot weight (cheat days). Below is my training program and my typical diet:

Monday: running (45 minutes), cycling (30 minutes) stepping (15 minutes)
Tuesday: rest day
Wednesday: rowing (1h15 minutes)
Thursday: weightlifting
Friday: running (45 minutes), cycling (30 minutes), step (15 minutes)
Saturday: rest day
Sunday: rowing (1h15 minutes)

And my typical diet (lot of carbs at breakfast and lunch and hyper protein for dinner with some treats I.e. Beers, cider or chocolate):
Breakfast: two toasts of peanut butter with one coffee and one tea
Lunch: one baguette of chicken, tuna or eggs and one treat plus coffee
A beer at 19:00
Dinner: tuna or eggs with vegetable and dressing plus a treat (another beer or a chocolate) and hot chocolate

Do you think I don't eat enough? My TDEE is around 2700 kcal. Should I eat more in the breakfast or dinner?

Thanks for your advise,
Jamal