Why am I having problems conceiving!?

It makes me really sad I have been married for almost a year but TTC for 2 years now.. And nothing happens. I am irregular so I know that makes it difficult and I don't have the best diet. I have completely removed soda and sugary drinks off my daily nutrition intake I only drink water (6mons now) I don't do drugs smoke or drink! This is just depressing! I get very sad and frustrated when I am late and my pregnancy test negative! What am I doing wrong!?