I've been having some serious bowel issues?

It seems that for my entire life I've either been constipated or had diarrhea, with just a few breaks in between where I've been regular. I eat very well. I eat plenty of fruits and vegetables, so I have a good fiber intake. I thought for a while that I might be allergic to something I'd been eating, which might cause the diarrhea, but there is no pattern at all. So, I have absolutely no idea what is causing these problems, and I'm worried that these might cause other health problems in the future. I've researched what causes this problems plenty of times, but none of the causes seem to be something that I've done. Is it a disease, like IBS or something similar? Can it be helped? I'm at a loss at this point. I've even spoken to a doctor who didn't provide a very good answer.