I would ask one question and then I will give one comment.
First, do you have any signs that your slightly-low fiber is having a negative effect? If you are not having any problems in the bathroom department, then I would honestly not worry about it. I was having problems with haemorrhoids (yeah, yeah, too much information) whenever I went for an especially vigorous jog. Despite the fact that I typically have 30-50 g fiber per day, my doctor recommended a fiber supplement to help (as if a mere 3 more grams would actually make a difference???). Not only did it not help, but I immediately shot up 10 pounds and it has been a difficult time to shed it. Gee....and now I just don't run so hard anymore and haven't had any problems down there in months. The idea that you need to eat a certain amount of fiber despite no negative symptoms is brought to you by the same people who suggested that trans fats were better than butter, eggs were bad for you, sugar was not the cause of diabetes and stretching before exercise prevented injury....all shown to be desperately wrong by follow-up studies.
Second, I would highly recommend that you try eating more fibrous foods (veggies, ground seeds and avocado come to mind) before you go for a fiber supplement. You haven't experienced discomfort until you burp up one of those nasty half-digested pills or some fiber added to a drink.