ohhh you poor thing. I do empathise....my DD#2 is 16 months, and whilst she will sit in the pram for a while, mummy enjoys the shops and im afraid 1 hr max is the most i can be out.
If i have to buy a present for someone, or need to concentrate (as most women do when they shop ) i buy DD#2 a chupachop. I know, i know, its not the most nutrious thing, but it does keep her happy for 20-30 mins.
Ive also just purchased a 'cleanshopper' - a material seat cover for shopping trolleys. I find she can look around more in a shopping trolley, and i can talk/sing to her too.
Good luck !!