Trackpad misbehaving - doesn't like tap/gestures

I've had my beloved trackpad for a while and recently it's started misbehaving. First it wouldn't respond to my fingers at all and would only select in the corners of my screen, as in it would snap hard left or hard right. I changed the batteries and it seemed ok.... BUT then it did it again, and now, while I can navigate the cursor around the screen, I can't tap or use multi-finger gestures to scroll or switch screens. I have to use the hard physical click to select something. I've checked the preferences and the multi-finger gestures are switched on. I've also changed the batteries over again.

Do you think this is a fault? I can't think what else it could be.

Thanks for your help!