What Causes Inter Menstrual Vaginal Bleeding While On A Birth Control Pill?

I am experiencing a bit of abnormal bleeding. I am not sure if it is my birth control causing it or if something is going on. I have had my period 3 times in one month which has never happened before (in my 3 years of getting the birth control shot). Also, my actual periods, the ones I keep track of that I get once every three months, have been getting longer.. They last about 2 weeks. When I spot/bleed in between scheduled periods it is normally heavier and clotting. I normally start to spot about one or two days after having intercourse more than normal with my boyfriend. During these spottings I get the same symptoms that I would if i were on my period. The cramping, cravings, and breaking out. I also sometimes feel pulsing in my right ovary, almost like a heart beat or twitching.