See your GP ASP because that was my only symptom and it turned out to be a 5 cm tumour, i had literally no other symptoms until then , he will probably give you a fit test and possibly see a consultation then a colonoscopy to investigate , i have since had an operation to remove the tumour and i am now having chemotherapy for three months, i know what i have put seems a bit alarming but it mirrored my experience don’t leave it as if it is then it will only get a lot worse if they can get it early things will a lot better, hopefully it isn’t , good luck and let us know how you get on