It is never easy to be good at anything, it takes effort and lots of hard work. But any work that deals directly with the public is even harder because you have to stand their attitudes and rudeness and still keep on smiling.
Beign a teacher (or a trainer) is tough and takes more hours than people thinks. It doesn't matter how well you know your subject. Even after all these years, I need at least 5 hours to be ready for just 1 hour of class.
Now you can't force anyone to learn if they don't want to. If you're doing training to adults, you have to realize that they're responsible for their actions. The only thing that you can do is to "seduce" them to do their work. Your students needs to participate in the class. As an average, a human only pays attention for around 10-15 min. Therefore, to engage them and keep their attention, you need to do an exercise or ask questions every 10-15 min, something that they can participate in, that also emphasize the concept that you're trying to explain so it is more memorable and easier to understand.
Finding a good example or exercise is hard, I tell you. And if it has to be entertaining, even more.
Also, you need to constantly ask for feedback. Once you've explain the concept and done your exercise, then you need to make sure that they do understand. Ask them "Is that completely clear?". If they say yes, then there's nothing else that you can do.
edit: Of course, if you don't like teaching this will be torture. So I suggest that you try to find some other position that you can enjoy more. Talk to your manager/superior so this part of your job will not go forever and ever.