Most back pumps are associated with Superdrol or PH cycles. I takeand (I Think). Are you drinking a lot of water. You might be getting a urinary tract infection. It's not because of something you have done it just happens. If it feels like someone is kicking you in the lower back it could be. Are you having any discoloration or difficulties urinating? Does it feel like when your done your not empty?
Back pumps usually last a day or two till the supp's kick in.