Hello,
This is actually a site about IBD - Inflammatory Bowel Disease, not IBS - Irritable Bowel Syndrome. You can learn more about IBS here:
www.healthcentral.com/ibd/irritable-bowel-syndrome.html
That said, I have both IBD and IBS so will give you a few pointers. First, you should see your doctor to discuss the change in your bowel habits especially since your father has IBD. IBD can be genetic so the most likely first step may be to find out if you have IBD. Be sure to tell your doctor about your father's IBD history.
IBS is considered a functional disorder of the bowels and typically symptoms include what you are describing - diarrhea, constipation, gas, bloating, and cramping. Stress can be an IBS trigger as can diet. If you are eating a poor diet of fast food, processed food, a lot of red meat, or foods loaded with sugar and fat this could be a problem.
You may want to read some of my Shareposts on this site about keeping a food journal. Basically, write down EVERYTHING that you eat and note how you feel physically and emotionally. Do this for at least 1 month and if food is causing some of your issues you will be able to see a pattern form.
I also have Shareposts about various diets that people with IBD tend to find successful in treating some of their symptoms. These may be helpful to you as well.