Extreme back pain 2 months after having my second child?

I had my son almost 3 months ago. I had an epi it went great, I had one with my first as well. I am now having the most extreme back pain to the point where I shake and vomit from the pain. The pain goes around into my lower stomach and I think that it is a nerve being pinched.I went to the ER and they gave me a shot but I don't want to go every other day for it. Is there any thing I can do to help with it. Has anyone ever had this? Is it from my epi? I really can not explain just how bad the pain really is. I lost my insurance when I quit my job and can not spare the money to go see the doc. any advice would be so great!!!!