Could this be a Urine Infection?? It doesn't hurt to pee though. :/?

Hi for the past 2 days i have been peeing constantly. There is so much pressure in my lower stomach and my lower stomach hurts constantly. But it doesn't hurt to actually pee. It is bewildering me as to what it could be. I have bowel and stomach problems that the cause is yet to be found but the pain is different so i know it isn't that. I am always constipated so could it be putting strain on my bladder? I had the runs all last week and then it stopped and i didn't go to the toilet for 3 days so i took some lactulose and had the runs again. But today i can't go yet i need to. Any ideas?