What Could Headaches After Epidural Shots For Chronic Limb Pain Indicate?

HI, I have epidural injections to alleviate chronic pain in my arms and neck. I had one 3 weeks ago and travelled 1850 kilometres to pick up some merchandise. I was fine on the trip up and also whilst I was there but the trip back I was very uncomfortable and have had bad pain and headaches(which I get at night in bed) . Why would this be . I was a passenger not the driver. Jan Martin