Think periods may be re starting

Hi all, I came off my injection in October as I had that one but never went back in January for another. The end of April I bled for one day only. And this month on Friday just gone I started to bleed, it got really heavy at one point but I'm still bleeding now but light? Can anyone suggest if this could be my periods returning ? As during the last 2 months I've had an awful pain behind my nipples and bad stomach pains. All ovulation and pregnancy tests are negative. Would appreciate replies thank you xx