BC shot

Liza

so I had the birth control shot about 2 1/2 months ago and I'm due for a new one here soon. My doctor had led me to think I wouldn't have my period for those 3 months. I didn't have one the first 2 months. Now at the 3rd month I've had my period for 3 weeks straight. When before the shot I've never had it more than 5 days. could something be wrong??!!