Which Jasmine do you have and is it growing in the ground? Do you prune it at all and if so, when? Does it produce any flowers usually?
For general info, if its Jasmine officinale and its in the ground, left unpruned, they flower prolifically as they age - but smell strongest in the evenings when its hot, you may not notice the scent during the day at all unless you're very close to it, but on a hot June night, the scent fills the garden.