Nobody ever said it was easy - but try to remember that every time it gets a bit hard you are learning heaps! All this is going to be so great in later years - not just for you but for all the animals you don't know yet.
As for right now...try to think of your anger and frustration in a different way. Be angry that Simba is in pain, but reassure yourself that YOU can help. Put yourself in his position - if you had a very sore and infected ear and someone esle started to make the pain worse without being able to tell you that it would make it better in the end what would you do? Not let them anywhere near you, right?!

As for the hard lump on his shoulder, very, VERY rare that any hard lump in that position is anything at all to worry about. Relax, get the vet to take a look at him and while you are there get him to show you how to put a tape muzzle on so you can treat the ear without any upset. It will hurt him for a few days but it will only get better if you keep the treatment up.