Will my asthma inhaler stop working if i don't use it for 3 weeks ? i mean will spray malfunction?

Prime it: Some inhalers requires priming with the 1st trigger mainly to fill up the delivery sprout and thus will not deliver medication. On the other hand if you were using inhaled steroid as a controller drug, it may not work after 3 weeks either due to loss of asthma control from the lack of medication or the fact that it takes 2-3 weeks for it to give you optimal results.

Unlikely: As long as the inhaler is intact and still has doses left, it should work properly when you need it. Storing it upright would be wise.