depo shot

So, my depo shot expired yesterday, and I made the decision to let it expire because my period was so weird and i was so tired of it. Also, the depo shot made me very sad and depressed. Anyways, my husband and I had sex this morning and he finished in me. I, genuinely, forgot about my depo shot expiring until later on throughout the day I was like fuck! My question is, should I be worried about pregnancy? I know my body still needs to get back to normal and such. Or should I buy a plan B?