Problem with Whatsapp, Help please?

I have a Samsung galaxy star 2 plus. Three months ago I updated my whatsapp to the latest version. I noticed that the newer whatsapp doesn t notify me of new messages until I manually launch it. Also my chat wallpaper takes seconds to load. Thinking that the problem is with the newer update, I reinstalled the version (older) I was using before; which worked perfectly well. The problem is that its going obsolete in a few days so I updated to the latest version- it doesnot notify me of new messages until I manually launch it and the chat wallpaper takes time to load. I contacted whatsapp and tried everything they told me to but the problem still exists. Whatsapp is my main source of communication, I will appreciate it if someone tell me what to do. Thanks