I Have Been On A Nur-esterate For 5 Months And

I have been on a nur-esterate for 5 months and having my periods as well never missed my date for injection until December when I had my last period I was suppose to have one on the 31st of December but even now I haven't had my period, I have periods pains but no bleeding; my lower back is painful, feeling some cramps on my stomach and I took 2 home pregnancy tests and they came out negative, I started jogging last month but gaining weight could I be pregnant?