Been on depo for 4 years, never had a period nor spotting but now out of the blue i got pinkish spotting with abdominal cramping n sore breast why?

Vaginal bleeding: Perhaps you need a different dose of depo-provera, but except for sore breasts, these symptoms could indicate an infection, such as an STD. Any new or unexplained vaginal bleeding or spotting, and certainly with low abdominal pain or cramping, requires professional evaluation. Get seen soon; do it today if severe pain, any fever, or if bleeding becomes heavy.