Yes! I'm also 43 and female and it sounds exactly like what I was experiencing (apart from the lower back pain), before being diagnosed with ulcerative colitis following a colonoscopy. 
 

My mum died fairly young from bowel cancer, so I was convinced that's what I had. I'd had bleeding on and off for years but had put it down to a fissure. It was a big explosion of blood that finally made me get it checked out. 

I'm now on intermittent medication to combat it and most of the time I'm fine, but I do still get that lower left side pain sometimes (these past 2 weeks actually) which tell me that I'm starting a flare and need to medicate before it gets worse and the bleeding starts again. It's a completely manageable condition for me, so I'm hoping that you will also find out that it's not what you fear.