What Causes Dark Periods And Swollen Stomach?

hi, i have had 2 periods in 2 weeks & the latest is dark almost black blood & my stomach is swollen, i have had 5 regular (every 28 days exactly) periods since coming off the pill injection - depo which i was on for 10 years,(periods resumed after only 3 weeks of coming off it!) is this somrthing to be concerned about? many thanks.