is there any difference in how sugar and food taste if your nose is blocked? if so, why might this be happening?

The food does not taste different but less as some tastes are not recognized because they require both taste and smell sensations to be recognized. Both the sensations taste and smell are closely linked and communicated to the brain where their information is integrated.

But as the receptors of sweetness are located on tongue only, it will be identified by the person even in blocked nose.