First of all, I think all teachers find it difficult teaching demanding and picky students. It’s not only new teachers who find this a challenge; so you’re not alone.
I think you need to speak to someone at the school, a head teacher or other such person. Tell them what you’re experiencing and do as you have done here: compare it with your previous teaching experience. Ask that person if they have any tips for dealing with the class. Try not to be negative about the class; just explain that it's different to your previous job and that you'd like some advice. Your first experience was successful, with time and a bit of support, you can make a success of this job too.
Some general ideas and tips:
Use a good course book to reduce the amount of time you spend on preparation.
Think carefully about the type of task you set for homework to help reduce the amount of time you’ll spend marking it.
Take the pressure and attention away from yourself in class; use a lot of pair work and group work. This doesn’t mean you’ll be doing nothing, it just means that the focus will not be on you.
If a student is asking for too much help, just say: ‘I need to go and see that student over there; he needs my help’. Use this tip judiciously! Don’t ignore a student who really does need your help!
Try to recycle classes as much as possible: re-use old lesson plans.
Finally, I’m afraid that getting questions from students after class is part of the job; as teachers it is something we have to do. You could think about setting aside 5 minutes at the end of the lesson for students to ask questions.