Stomach worry and period

well 4 the last 6 wks I have bein very constipated I have tried takin prune juice which only helps abit. my periods r usually very light but this time it as bein a bit heavy wit red jelly lumps. I am gettin lower stomach and back pains 4 about 3 wks now and lst nite I got a very bad headache which I never got b4. I am on the pill 4 8 months now. I had the injection in arm 4 3 years only had period about 4 times. should I b worried/

You shouldn't worry until you have some accurate information that says you have something to worry about. Make an appointment with a doctor.