i have always had symptoms similar to asthma(coughing and tightness in chest after running) but these only happen when i really overwork myself. i was wandering if this is asthma or not, and if so whether its worth going to see a doctor as it doesn't affect my life much, but some websites say that asthma can get worse over time.

It sounds like it maybe exercise induced bronchospasm – ie when the muscles around your air tubes tighten and make the tubes smaller. Asthma can be quite difficult to diagnose conclusively especially if you don't have any other symptoms – it doesn't necessarily get worse over time. Asthma is defined as variable airflow obstruction and can be well controlled on the right medication. You could go and see your gp (or practice nurse specialising in asthma) who may suggest doing an exercise test and measuring your peak flow – or getting you to keep a peak flow diary at home. They'd need a bit more info to assess whether you might have exercise induced asthma, like whether this is a new problem, if there is a family history of asthma, if you're overweight, if you smoke etc etc. from that they could decide if it warrants further investigations. Hope that helps. Try checking out Asthma UK – its a good website.