Pit of stomach feeling - HELP

sounds like diaphragm, respiratory fatigue and/or reaction to acidity.

try not to begin your tempo or longer interval training with

coffee or soft drinks in your stomach. caffeine increases the work of breathing. keep water on hand, and make sure you are at least moderately fueled. being fueled will lower your threshold but at the same time support superior performance. the acidity and caffeine is not always helpful, can add to heat stress and trigger some reflux. remember the response in a tougher session is additional epinephrine, and you likely require little boost anyway since you are passionate about your running anyway.

the second part of the answer is the emotional aspect. pressure is good, but too much pressure is not sustainable.

accept your fitness level and your efforts toward your goals.

this is sport, not war. however far you go in the sport, remember this is supposed to be fun. the great running days will come, sometimes even when you don't expect them to.