I Only Had One Depo Shot I Was Due To

I only had one depo shot I was due to go back for another shot a month and half ago and when I was on it I had non stop bleeding maybe once a week I wouldn't bleed for a day now it's been a month that I've been off it and about 3 weeks ago I started bleeding/spotting brown and sometimes alittle bit of red in it.. It sometimes would stop for a day then I'd spot just alittle bit of pinkish blood but barely any , it's been more then 3 weeks and it still hasn't stopped. Some days it's lighter then others but still there. Also I've been having unprotected sex since the shot has worn off