Periods after Depo needle

Hi,  I've noticed this is commonly asked but I have not had my period since my depo needle ran out on 23rd Feb. I stopped the needle mid last year and then went back on it a week after I met my partner in august last year. I had no problems or period at all with the depo and then it ran out mid November and I usually would get some bleeding coming off the needle but I didn't. I had the needle 3 weeks after it had ran out on 1 Dec. Soon after the needle I had bleeding and pains and I took the pill occasionally to settle it down. I have put on over 15 in the last 3 months. When my needle ran out on 23rd Feb due to all the weight gain I've decided to try an alternate contraceptive, however I was waiting to get my periods until I start but it's been 44 days since my needle ran out?? What could be the explanation??I have had pregnancy test but they have been negative.