How long does it take for an antidepressant to work?

i started on allegron/nortriptylene two and a half weeks ago. Since then I haven't seen any change in my depression but I believe the medication is causing me to feel more depressed and irritated. I don't know if these feelings will go away in time if it hasn't kicked in yet or if It's just not working in which case I will stop it.
How long does it take for an antidepressant to work?
Post Opinion