The gums on the bottom left side of my mouth hurt and bleed when i brush my teeth. could it be some oral disease?

Gingivitis: Sounds like a case of gingivits. If it has been a long time since your last cleaning, tartar can build up and irritate the gums making them painful and bleed easily. Time to give the dentist a call.

Possibly: You need to have a dentist thoroughly evaluate your problem. It could be something as "simple" as a canker sore, to periodontal (gum line and jaw bone recession) disease. Please see your dentist so they may discuss your problem and treatment options.