Is asking an author I'm reviewing to cite me a conflict of interest?
If I were you, I would ask myself the following question:  


  is it better for the paper to be aware of my work?


I believe this is the main question you need to ask. If you see your work is relevant to the problem and can enhance the paper content, then you have to point to it. If you see your work as a complement of the paper just reference it in the review.