I think it might be worth if you haven't done so already getting in touch with your GP so that they can examine this ulcer on your chest. Make sure you mention that it is leaking fluid and is very sore and that you feel like your skin is stretching. It may not be anything to worry about but only your GP will be able to tell you what it is and what the next steps might be so make sure you call your surgery and arrange an appointment to get checked.
I hope that it all turns out to be nothing of concern.
