Back pains after baby?

I keep having these bad pains in my lower back, my daughter is 18 weeks now and ive had them pretty much since she was born, at first i put them down to my body getting back to normal but i think there going on far to long. Its hard to describe but there painfull stabbing twinges next to my spine, i did have a epidural and i wory that the pains are liked to this. They are at random times during the day and only last a few seconds, some days ill have loads and others ill have none. i have been to doctors and she said to go back if it got worse (what a pharse) she seemed very patronising when i mentioned that i think it may be from the epiduarl, what do you think it may be? thanks