Oh, you poor thing, how ghastly.
I did my back in, and it spammed for weeks as I stupidly didn't go to the doc immediately. When I did I was given diclofenac, but was told I could use paracetomol and neurofen as well. I took the diclofenac 3 times a day, and in between doses took one paracetomol and one neurofen (they're both more effective if you take them together). I was also given diazepam as a muscle relaxant to calm the spasms.
I also took Zydol for a few days, but reacted very badly to it. If it works for you, though, I understand it is a miracle-worker of a drug.
I didn't know you take diclofenac when breast feeding and don't know if you can take any of the pills under those circumstances (except paracetomol, obviously, which is fine.).
I do hope it calms down soon. Hot water bottles? Sometimes lying on a packet of frozen peas does it a lot of good too. I used to find that really helpful. I just lay down on the floor with the packet stuffed under the worst bit of my back, and watched tv for an hour or so.