Firstly just review your diet and check for any red coloured food products that may be causing the red colouring (beetroot is the favourite) It's amazing how many foods can play havoc with poo.
You are right to call your doctor and blood in your poo is a common issue, which has many causes.
Fresh blood is usually from the lower part of your bowel. It can be from haemorrhoids (piles) If you have been straining for a poo, are pregnant or sitting for long periods of time. Veins lining your intestine near your poo hole can become engorged and bleed a little when you go to the toilet, particularly if they are irritated.They are annoying rather than life threatening, and chemists sell anaesthetic cream for them.
Dark tarry poo or dark tarry blood is usually a sign blood has been partly digested higher up in your intestinal system. That can be from infections, tumours, ulcerative sections of bowel. There are many causes.
So easy to say if its not you - but don't panic. There will usually be a simple explanation, and you are doing the right thing getting this checked out as soon as you are worried.