Beetroot juice gives a boost - loads of articles online about its stamina enhancing qualities. I use that pre-packed organic beetroot from the supermarket to create various smoothies. Banana and beetroot with soya milk a particular favourite
It's difficult for you to judge how your foot is hitting the surface when your on a run. Plenty of running shops video your running action in-store and supply footwear that corrects pronation issues. Avoid the £20 bargain stores and pay a bit extra for some specialist help.