I'm a bit confused:
Your saying your tierd after 2 mins but carry on to do 30 mins? are you sure your tierd (as in could sleep) rather then feeling aches and pains or warming up- do you warm up properly first? 10 mins should do it, start slow, then get faster. No need to stretch but work on moving the joints about a bit (e.g hugging one knee at a time whilst standing, lunges, touching your toes or touching each toe with the opposite hand -right to left, left to right- whilst keeping legs straight...etc). Run stop, run stop run stop, 1 min on one min off....etc
Warming up is important and required.
Do you also wear a Heart Rate Monitor? if your concerned about your chest pain, this could help reassure you- are you sure its heart related or lung related? Oxygen is required to circulate the muscles as we exercise.
The harder we go, the longer we go, the more oxygen is required as the blood circulates at a faster rate.
If we have poor lung capacity we find it hard to get that oxygen to circulate which can lead to muscles feeling fatigue as the lactic acid (naturally our muscles produce lactic acid as we exercise) the lactic acid in our muscles which isn't being expelled from the muscles can cause pain and fatigue.
The way around this is to exercise more and more frequently- not to go overboard and make exercise endless but to exercise maybe little and often. This helps to build lung capacity and also to develop the heart: our hearts are muscle and the stronger they are, the more they can pump blood filled with oxygen and nutrients around the body.
If things hurt too much, calm it down a bit- only you can decide if this is what you want to do, its your body, your pain threshold and only you know best. No one can give or take permission away from you to chose if you want to do that, its up to you to decide.