Martha, I'm a lapsed Catholic but still consider myself a Christian and a Catholic (with an open mind). When I went to Mass on a regular basis I usually picked up good energy. At one point, I think the biggest doubter was the priest! I don't think I'm as sensitive as you. I'm a newbie anyway.
As somebody once said, a church is a hospital for sinners, not a museum for saints. So yes, you will find all kinds of people in a church. As far as shielding yourself from bad energy, I don't know how to do that myself yet.
If you choose not to go to church regularly, I don't think that's sinful. It says to "honor the Sabbath day and keep it holy", but I don't interpret that as meaning physically going to church. If it's draining you, that's not good. I guess what I'm saying is you shouldn't feel guilty, whatever your decision. But I don't think Jesus wants you to spend every Sunday feeling drained and exhausted.