Only have bowel movement once a day same time before i used to go 2 times i've had lactulose today i had the runs it won't be anything serious will it?

Hard to say: Although a change in diet, meds, exercise, hydration, health, caffeine, & stress all affect frequency of BM, we typically say that if there's a change in bowel habits, get a colonoscopy since it can be a symptom of a colon tumor (which can be removed before it becomes cancer, or if cancerous then hopefully before it spreads). Level of suspicion depends on risks, so get seen to see if needed.