I have diarrhoea and sever pain on my bottom left side. Now the diarrhoea is bloody. I'm weak and have hot an cold chills and a pounding headache? What could be the cause

Infectious diarrhea. Bloody diarrhea is usually due to an infection of the digestive tract. Given your symptoms, you need emergency help. Get to an emergency room immediately, by ambulance if necessary. Good luck, but don't delay!
Diarrhea and pain. You need to go to the Emergency Room if it is what you describe. There are too many things this could be to try and diagnose without a good exam and labs and possibly radiology testing. This could be infection, abscess, fissure, diverticulitis, colitis or other issues.