In my last few runs I have been experiencing a pain in my left chest. It's quite sharp, but not shooting, and it gets better / worse as I slow down / speed up. It's not something that stops me running but it does make it uncomfortable - especially during tempo runs. It's been like that for a week now and I can feel a "presence" now even when not training. It feels as though something is lodged in there but it's nowhere near my digestive system.
Has anyone experienced this? Any ideas on what's causing it?
(I've recently increased mileage recently by about 15% to 63 p/week - I'm 29 years old and have been running about 2 1/2 years).