I am suffering from leg pain for one month with some weakness in my legs. however, there isn't any problem walking on those legs. what could be the problem?

Many possibilities: The potential causes of these symptoms are innumerable but most commonly are the result of lumbar spinal conditions. You should consult with your physician to determine the cause.

May be spine: Could be a disc protrusion or herniation. You should see a spine physician. An MRI of your lumbar spine would help rule out nerve entrapment from a problem like this in your spine.