I really feel for you as anal fissures are terribly painful. I had one earlier this year and the pain and bleeding was horrific. I ended up seeing a specialist for mine. It eventually healed on its own by using Rectogesic (this might be the cream you were recommended..I don't think it's safe to use when bf), wet toilet wipes, salt baths, metamucil capsules (2 in the morning and 2 at night) and drinking lots of water.
It was taking a long time to heal though and the next step the specialist recommended was botox injections. He said they have good success with botox for anal fissures now.
If using less invasive methods isn't helping, ask for a referral to a specialist. I saw a gastroenterologist and he was lovely about it all. I'm sure they will be able to help you, you shouldn't have to go through that kind of pain.