why does my intergrated fridge keep defrosting?

Your fridge is suffering from the same problem that hundreds of other integrated fridges suffer from, ie. it is not getting enough ventilation to cool down the refridgerant in the cooling loop at the back of the fridge. The result being that warm refridgerant is entering your fridge-hence the defrosting
The adjacent oven wont be helping but at this time of the year fridges work harder and need as much circulation air as possible around the rear radiator.
Have a look at the ways this can be improved by looking at the bottom air intake and top air exits to see if there is room for improvement.

This is the reason why the Americans drag their fridges out onto the porch during the hot season

Geoff in Wales
August 2011