I am in my last year at school so behaviour problems aren't really an issue any more, but in the younger years, it obviously was. The best teachers never had to really raise their voice to shouting level, but gained respect some other way... I think a lot of it was reputation... As soon as you have a reputation for being 'weaker', and unable to control the class, it's difficult to recover. One of the teachers at my school did teacher training at a school only a few miles away, and it just so happened that one of my friends used to have him and said he used to struggle to get a decent level of discipline, but at my school now, he is pretty average. I think a sense of confidence, feeling you have control and authority, and trying to treat the bulk of people reasonably are a few traits found in good teachers, although it is hard to pinpoint how some weak old short lady can control a class while a young, tall man struggles.
Oh and generally, IT teachers struggle. In all my years at school, I haven't had an IT teacher who had enough control of the class to stop people browsing the Internet in lessons... Some of them didn't even bother trying. If we had an English lesson in an IT room, the English teacher would struggle a lot more... It's a pretty hard lesson to teach I guess with such a massive potential distraction.
I hate that feeling that you've tried really hard, and you really really want to do something, but you can't... It is really depressing. I guess you just have to think about something else you can do instead... Can you not work as a software developer or something else? It is quite likely that over time, you will improve and get used to it, but if you don't already have that control, it will quite likely take a long time, and do you really want to be spending years struggling to control the classes??