persistent bowel issues at 20 years old male

Hi,

Since the beginning of March I've been having constipation when going to the toilet, at one point I had found blood in my stool which was bright in colour but only happened once, I got in contact with the GP at the start of April and was given laxatives. This constipation continued until May 1st, which I had woke up feeling nauseated and had really bad diarrhoea, nausea has since gone away but the diarrhoea persisted, I got back in contact with the doctor which I was given a rectal exam and a full blood count, which all came back clear which the GP said was really reassuring. The part which is now concerning me the most is the GP referred me for a colonoscopy urgently. Which when I heard the word urgently I've managed to convince myself it's going to be something serious like cancer.

Has anyone else been in this situation that could maybe shed some light and offer some reassurance?

Thanks