There is an art to training and if you want I would be happy to email you a simple training plan for a sprint triathlon. It sounds like your weakness is the muscular endurance on the run which is a typical weak spot for many triathletes. I have been racing tri for 3 seasons (my focus is Ironman) and cycling competitively for 17 years. I have some very simple plans that I could send to you. Just email me offlist.