Newbie Composting - No heat in my heap

I've stopped adding to my heap because all I can produce in any great quantity at the minute is grass cuttings. It seems after I add grass I get a couple of weeks of heat and then its back to being cold. Is this normal?

I turned the heap tonight for the first time in a couple of weeks and it looks a nice dark brown colour but is along way from looking as fine as the compost you'd buy.

 

I add cardboard, newspaper, even paper bills/statements.