I think it was inevitable that Gladys over protect Elvis when she lost his twin..she didn't want to lose him too. I think it also had to do with the hard life she'd had growing up. Also after all I've read I believe she suffered from post partum depression. That can go away on it's own or it has to be medically treated and they didn't know about that when Gladys had Elvis so she may have had it all her life. That could very well explain her nervousness and her constant worries.
As far as Elvis' affection towards his mother, I think they were perfectly normal under the circumstances. He wanted to protect and take care of her....make everything all better for her.