Pregnant? Impossible

I had my first born baby on July and got my first birth control shot on 22 Aug, it's every 3 months injection. I never go for my second shot... cause I don't like the side effects, it's bad than I thought. Recently, I felt fatigue...like really tired. Started to feel pain here and there. Sometimes dizzy, I don't suspect pregnancy because some people said that after taking the last shot it will take some time to get pregnant again eventhou if you've stops. I really can't tell much as my I don't have regular period (the effect of the shot) only spotting till now so pregnancy would be my last thought. Possible ? I'm curious, husband told me to go check up but I don't want to disappoint him... he really want a number 2.