Read your email and you pretty much answer your own question, look:
I am fed up of doing the same routine in the gym over and over and not developing any further
Got a clue yet? :)
You need to change your routine. I am not sure what exactly you are doing, but if you want to get bigger and actually look a lot bigger in your clothes then try and train more like a Powerlifter than a body builder. Do heavy, basic compound movements and leave the small stuff like dumbbell curls aside. Concentrate on increasing your weights each and every week.
So for example on a Monday do Chest (heavy Bench Press), Shoulder Press (heavy overhead) and maybe some heavy triceps pushdowns. Leave Tuesday aside for rest and eating.
On a Wednesday, do heavy back work, such as Barbell Rows and leave things like lots of dumbbell curls aside. The truth is that if you are lifting a lot more on the heavy exercises, then your arms will be getting bigger anyhow.
Don't train your abs for now, as ab training has a detrimental effect on overall size. Make sure you train your legs hard and heavy with lots of heavy squatting. Keep the weight high, form good and reps low. Do this once a week. Squatting can add at least 10% to your overall upper body.
Food-wise, if you want to look like a big guy, you need to eat like a big guy. Think about this. Read it over and over again. If you want to look like a big guy, you need to eat like a big guy. I mean REALLY EAT! So you would maybe make a big bowl of pasta and chicken the night before and have that at least 4 times the next day alongside your regular meals and protein shakes. As much as you can and if you are training hard and heavy, you will find that you won't put much fat on.
Drink lots of water each and every day. Don't neglect protein and for god's sake stay away from known estrogens like alcohol, soya, cannabis. Make sure you don't get stressed either as stress kills off muscle tissue and gets you fat. If you get stressed by people, just walk away. If you get stressed from work, think of nice things and get your mind off the stress. I would say avoiding or reducing stress is as important as doing a good set of Presses in terms of muscle development.
Good luck!
DOC YO