What Causes Lower Abdominal Pain With Streak Of Red Blood In Stool?

Hi, I am a female aged 39. For the past few weeks i have noticed that there is often a streak of red blood on my stool, the first half of my stool is very hard and bobbly, followed by a very loose half. I have been having stomach ache and the lower left of my abdomen is tender, I seem to be passing rather a lot of gas at times.for the last four/six years i occasionally get a severe stabbing pain deep inside my bottom, my bottom is rathe itchy too. I experienced this three years ago and had a colonoscopy which showed no abnormalaties. I am physically well but suffer from depression, for which I take duloxetine.

Last time i was told it was caused by irratable bowel syndrome, could you advise if i need to investigate this further.