Many things at once.
The best treatment for a lower back strain is icing immediately (then switch to warmth after 2-3 days), Ibuprofen
, and keeping active.
In the past, people would be in bed all day after a back strain, but now we know you can actually decrease pain by being up and mobile, walking and doing normal activities. Don't be surprised if it takes 2-3 weeks to feel better! good luck!