Depo Injection

Hi im 30 yrs old on went on the depo in jan 08 came off in april 08 to try for a baby it taken 3months for my period to go back to normal ive had regular periods since then.but ive not came on this month and ive also done 2 pregancy tests but both came back negative and i dont feel like im going to come on but my boobs feel tight and it hurts to where a bra. What could it be can someone help.