One other thing I forgot to mention is you may have a food allergy, which would also explain why your relatives have this, too. A common one that causes diarrhea are milk and milk products, so switching to soy milk or rice milk can help, they're in most grocery stores in a small carton in a special section of the store. Or there are tablets you can take with meals that will counteract milk allergy. Try keeping a little journal of what you eat and when your diarrhea is the worst, and that can help you narrow down foods that might be triggering your diarrhea.
You can go to your county health clinic, it's free, and have a doctor see you for your digestive problems, and he can provide treatment. Sometimes they'll charge a little if you work at a job, and it's based on how much you make, but it's still far less than going to a regular doctor.
That your relatives have this, too, suggests a genetic component, which can still be treated but may not be the run-of-the-mill viral or bacterial infection. So, I can suggest a few things to help stop the diahrrea, but it would just be a bandaid.
I had diarrhea just like you for six straight months, every day, half-dozen times a day, near about died. The prescription medication hyocyamine helped me. Also, eating Activia yogurt from the grocery store helped me. And eating 100 percent whole wheat bread, eat it as a sandwich with lettuce in it every day, will help bulk up waste. You can also ask a pharmacist at a drugstore what over-the-counter is real strong for helping diarrhea.
By the way I'm 130 pounds 5'10 and I cant seem to gain weight