I had random spontaneous bleeding in my mouth. what could it be from?

You should really see your dentist. Right now the best thing you can do for yourself and your oral health is to floss 1xday and brush 2xday. It sounds like you have severe gingivitis which is complicated by the anti-depressants. Anti-depressants can cause dry mouth, which will affect your gum health. It's very important that you maintain excellent plaque control, and have the condition monitored by your dentist, just to be sure there is not a more serious gum disease going on (which can result in losing your teeth).