Hey Bexi, My experience with my own anti-depressants is that if I miss a day, or especially several even if they're not in a row, I begin to feel a bit awful. Sometimes I have a bit of withdrawal, sometimes I just start to feel the old bad feelings coming back.
My Dad is also on anti-depressants and the same thing happens to him. He told me there is a specific dose that works for you, and if you take more, it won't make much difference, and if you take anything LESS, it won't do its job.
So when you skip a day, you're lowering the amount of the drug that's in your system, and it seems likely that that means there's no longer enough to be effective!
Don't miss your pills!! You could get your mobile to give you a reminder alarm each day at a specific time, or put a sticky note on your wall, or keep your pills beside your bed or somewhere you'll see them.