What Causes Tender Breasts And Stomach Cramps After Stopping Depo Injection?

I stopped my depo injection in December and have not had a period yet. I now have very tender breasts, a large swollen stomach and extreme cramping at night. I have taken 2 pregnancy tests both negative but I am unsure when to test due to my periods not returning yet. Is it possible that I am pregnant or could it be my periods returning??