Hi Arabella,
The most usual cause of a smelly compost heap is too much wet greens. Perhaps you have a lot of grass clippings in your heap? This is easily rectified by adding more brown materials, i.e., Cardboard, Newspaper, Egg cartons, leaves, etc.
Turn the heap from time to time, you don’t need to do this every week or indeed every month but by doing this you get air into the heap and the more often you do it the faster you will generate compost.
As for weeds, I usually don’t put them in my heap as you need to be sure the heap gets up to a high temperature to be sure to kill off any seeds.
Stuff you cant compost has to go into your refuse bin I’m afraid