first off how long have you been working out for? "quite some time" isn't really a time frame.
second, how much bodyfat do you have? or to make it easier for you.. do you have visible cuts? can you see ab lines or do you have straight up abs?
i guarantee that your diet and/or training is not in place. many think they have those down but they dont. by the way your sentence is structured regarding diet and eating "clean", you are not eating enough.
but hey, you're 28 you're a big boy. if you want to take steroids then by all means go do some research and stick that needle in your butt... but you will be wasting your money.
when a smart person decides to make the move over to this side their diet and training BETTER be in place beforehand otherwise, again, its a waste of money and your health. if you're gonna do it, do it right. good luck