We've all been there mate - I used to bladder the gym with my mate when i was about 18 (like we all did) then i got my desk job after uni and slowly and surely my belly and arse got bigger. I realised about 5 years ago i needed to do something about it, and started with P90x, then i had a PT, and trained with my mate.
I didn't realise what i was putting into my body though, and everything i was doing nothing was clicking until i sorted nutrition and what i was eating. I was making "noob gains" losing weight and looking a bit toned but nothing dramatic, then i sorted out what i was eating, when i was eating it and it sounds ridiculous but weighing everything i ate (raw) and within 2 months i started seeing better results.
now i look at things and thing protein fats and carbs and a rough weight, luckily i dont need to be as on the ball with weighing things and because i am in pretty decent shape now my diet (i say that even though its not a diet) is pretty relaxed to a point.