Depends on the cause of the pain. Alternate ice and heat, more ice though, anti inflammatory medication if you're not allergic, and rest....only way to let it heal.
How to relieve back pain FAST?
It depends on the cause of the back pain. Painkillers will help dull back pain to some extent, and if there is swelling, then an anti-inflammatory medication would be recommended.
Further than that, it really depends on the source of the back pain, and how it can best be alleviated.
If you are suffering from chronic back pain (that comes back frequently), or if the pain is still very intense despite taking basic painkillers, then you should contact a doctor, as this could be a symptom of several conditions.
There is no 'one' way .. There are a number of remedies but there are two things to determine first. Do you need to 'dull the pain' or do you need to 'fix the cause of the pain'.
Taking a pain killer, for example, sends a chemical to the brain that merely causes the brain to act in a certain way so as to reduce activity in pain receptors. Taking an anti inflamatory, on the otherhand, reduces inflamation that is causing pain. Once you reduce the inflamation the pain goes away. On the other other hand, Pain from a muscle cramp causing stiffness and soreness can be remedied by message.
Then of course, there are forms of acupuncture that can help with many sources of pain because it can treat pain AND what is causing the pain as well.
Ultimately, it is important to know what is causing the pain before you try to remedy it.